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Archive for the 'Home Field Advantage' Category

First time visitors, against the spread

Posted by Jason Lisk on November 11, 2009

Last week, I posted some quick numbers on the new stadiums from 1997-2003, and the winning percentage of the road team based on the number of visits they previously made to that new stadium. Commenter "Guy" had a concern about team quality:

Don't you need to account for the strength of these 12 teams, and the visiting teams? These twelve teams, in their 2nd, 3rd, and 4th seasons in the new stadiums (when many of the first-time visits must have occured), were a combined .564 overall. If you assume a HFA of 70 points, we'd expect them to be about .634 at home -- not that much lower than you found. If the first-time visitors happened to be slightly below average (which they likely were, since these 12 home teams are above average), that could account for the remaining gap.

As a quick correction, I need to point out that there were actually thirteen teams in my study, but I forgot to list the Houston Texans and Reliant Stadium, though they were included in the data set. But I'm sure Guy would have the same question even knowing the Texans were part of the data set, and rightly so. When I first began looking at this several months ago and then stored it away for a rainy day, I did not have "against the spread" records readily available. However, we do have "against the spread" data for all the games in question, so I figured I would dig back in and try to account for team strength.

3 Comments | Posted in Home Field Advantage

Road Team Winning Percentage, based on number of previous visits

Posted by Jason Lisk on November 4, 2009

I've spent alot of time talking about familiarity and home field advantage. Most recently, I wrote about the New York teams sharing a stadium. Today, I'm going to do mostly a data dump of other research I had done on the familiarity issue.

From 1997-2003, a flurry of new stadiums opened in the NFL, with the following franchises playing in a newly built stadium: Washington, Baltimore, Tampa Bay, Cleveland, Tennessee, Cincinnati, Denver, Pittsburgh, New England, Detroit, Seattle, Houston and Philadelphia. I pulled the results for those thirteen stadiums, in terms of how many times the visitor had previously visited. I didn't use exhibition data, but did use all regular season and playoff visits. These numbers are through the 2008 season and playoffs, and do not include results this year. The win percentage is the wins and losses from the perspective of the visitor.

Visit		W	L		win pct
1		134.5	242.5		0.357
2		60	113		0.347
3		50	54		0.481
4		29	34		0.460
5		20	30		0.400
6		19	25		0.432
7		21	18		0.538
8		6	10		0.375
9		7	7		0.500
10		4	5		0.444
11		3	2		0.600
12		2	1		0.667

These are the overall results. I divided the games out into divisional and non-divisional games. We know that divisional opponents get to play at a venue every year, whereas non-divisional opponents typically do not. There is a bit of a grey area when it comes to teams that were division opponents until the realignment in 2002. I treated games as divisional games if the road team was in the same division that season. So, Tennessee is a divisional road opponent of Baltimore for games before 2002, and a non-divisional opponent after 2002.

Here are the division opponent only results, sorted by number of prior visits to the same stadium:

Visit		W	L		win pct
1		22.5	31.5		0.417
2		17	37		0.315
3		28	24		0.538
4		24	23		0.511
5		18	22		0.450
6		15	24		0.385
7		19	18		0.514
8		9	9		0.500
9		6	9		0.400
10		7	5		0.583
11		3	2		0.600
12		2	1		0.667

There are a small number of games once we get beyond five visits, but the combined win percentage of division opponents when visiting these stadiums for the fifth time (or more) is 79-90 (0.467). Also, with a couple of exceptions, every one of those first visits by a division opponent was in the first year that the stadium opened. We see that the division opponents actually perform worse in the second season.

Non-divisional opponents, on the other hand, will tend to have their first visit to a stadium after the home team has already been playing there for at least a season. Here are the non-divisional results, based on number of visits.

Visit		W	L		win pct
1		120	211		0.363
2		47	78		0.376
3		22	34		0.393
4		9	12		0.429
5		4	10		0.286
6		4	4		0.500
7		2	3		0.400
8		0	1		0.000

If we exclude the first time visits that occur during the first year of a new stadium (when the non-divisional visitors went 24-29), then we get a 96-182 record (0.345 win percentage) for all non-divisional teams in their first visit to a new stadium more than a year after it opened.

10 Comments | Posted in Home Field Advantage

New Jersey, New Jersey

Posted by Jason Lisk on October 14, 2009

Last week on the New York Times Fifth Down blog, Toni Monkovic pointed out that Eli Manning has a better record on the road than at home as a starting quarterback. Several theories were posted in the comments, ranging from the winds at the Meadowlands to the Giants' fans behavior. One that was not mentioned, though, was the effect that sharing a stadium with the New York Jets may have on the home field advantage at the Meadowlands. In the past, I have written about the possible role of road team familiarity on home field advantage when discussing similar climate division rivals, when looking at the effect of new stadiums, and when looking at playoff rematches.

The two franchises have shared a home stadium since 1984, when the Jets left Shea stadium. The Giants had been playing at the Meadowlands since 1976. This situation is virtually unique in American sports. The only other situations I am aware of where two professional football teams shared a stadium at the same time (other than occasional games or emergency situations) were in the early days of the AFL, when both Dallas teams played in the Cotton Bowl, and when Oakland played in Kezar stadium, home of the San Fransisco 49ers, in 1960. And in those cases, the leagues and opponents did not intermix. The franchises will continue the shared stadium relationship when they move into the New Meadowlands complex next season.

14 Comments | Posted in Home Field Advantage

Checkdowns: More on Familiarity and the Psychology of Home-Field Advantage

Posted by Neil Paine on September 12, 2009

From Sabermetric Research, Phil Birnbaum looks at a series of HFA studies by Matt Swartz of Baseball Prospectus. Mainly it's baseball-related, but Part III is of particular interest to us here at PFR, because it looks at familiarity and distance effects, finding that HFA is lower in divisional games than in other league games, and lower in intra-league games than in inter-league games.

Longtime readers will note that such findings echo what we wrote about familiarity effects in these previous posts here at PFR:

Travel time and temperature part one and part two

The effect of new stadiums

Playoff teams that get to return to a venue they played in the regular season and a look at home field advantage in divisional versus intra-conference matchups

10 Comments | Posted in Checkdowns, Home Field Advantage

More on familiarity and home field advantage

Posted by Doug on January 15, 2009

Yesterday JKL posted some intriguing numbers concerning visiting teams' fortunes the second time they play in a particular stadium in a year. The implication was that, possibly, a nontrivial portion of that rich stew we call Home Field Advantage might be due to familiarity with the peculiarities of the venue.

I decided to follow up on this with another quick study.

In the playoffs, Joe Flacco tells me, there are no more rookies. And in the second halves of games, there are no more unfamiliar stadiums. Or something like that. What I'm getting at is: if familiarity plays a meaningful role in home field advantage, we might expect it to be most prominent early in the game.

Now, home field advantage seems to be greatest in the first quarter for all games in general. But if familiarity is a meaningful factor, the first quarter advantage should be even more pronounced in games where the road team doesn't visit the stadium often.

I looked at all regular season games since 1978 that were either:

intra-division games, in which the road team should be fairly familiar with the surroundings because it plays there every year.


inter-conference games, in which the road team should be mostly unfamiliar with the surroundings. This has varied over the years, but in the current scheduling format a team will visit an inter-conference opponents' stadium only once every eight years on average.

I want to emphasize that this is a pretty sloppy study. I didn't do anything to account for new stadiums. I didn't account for the fact that the Jets and Giants share a stadium. I didn't account for divisional realignments, which could create some unfamiliar intra-division matchups. And so on.

Disclaimers out of the way, here is the summary table. This shows the average point margin between the home team and the visiting team for the given time period.

                   Qtr 1    rest of game
Intra-divsion       0.78       1.86
Inter-conference    1.20       1.76
Difference         +0.42      -0.10

Inter-conference hosts got about 40% of their home field advantage in the first quarter, whereas intra-division hosts only got about 30% of it in the first quarter. Interesting.

Here's another fact: in the intra-division games, the home team scored first 55% of the time. In the inter-conference games, the home team scored first 58% of the time. That may not seem like a big difference. And in fact it isn't a big difference. But it's probably a real difference, and not just noise (p =~ .02, if you're into that kind of thing).

11 Comments | Posted in Home Field Advantage

The Boys are Back in Town

Posted by Jason Lisk on January 14, 2009

In one of the greatest Super Bowl upsets of all time, the upstart AFL Champion New York Jets beat the NFL Champion Baltimore Colts, 16-7, in Super Bowl III, to give the AFL its first Super Bowl victory and instant credibility. Let me give you an explanation you've never heard to make sense of such a game. The location was the Orange Bowl, where the Jets had played just four weeks earlier in the regular season finale against Miami. The Jets team played there in '67 and '66, too. Baltimore? They had never played a game at the Orange Bowl--never even played a regular season game in Florida.

Fast forward to last weekend, when the Arizona Cardinals traveled to Carolina, where they had lost by 4 points in the regular season. The Cardinals had struggled over the final month of the regular season, were 0-5 in road games played on the East Coast in 2008, and would be without WR Anquan Boldin. They weren't given much of a chance on the road, and entered the game as a sizeable double digit underdog. Two years ago, in my very first post as a member of the "staff", I predicted that the Arizona Cardinals would enjoy an increased home field advantage in 2007, with the rationale being that teams in new stadiums enjoy a familiarity advantage over road teams who have never visited the stadium before, particularly after the home team has had some time to develop its own comfort with playing in the new stadium. Over the last two seasons, the Cardinals have gone 12-4 at home (and one of those losses in 2008 was to a team who had previously played in AZ) and only 5-11 on the road, for the largest home/road differential in the league over the last two years.

In the first round of the playoffs, thanks to the rule that gives division winners with worse records the higher seed, the underdog Cardinals drew another first time visitor to University of Phoenix stadium, the Atlanta Falcons, and jumped on them early en route to a 30-24 victory. But the divisional round game against Carolina was on the road. Yet, despite that, familiarity may have still given the Cardinals an assist in reversing the regular season fortunes. Now, they return home to face another team that has never played a game at the new stadium, the Philadelphia Eagles. The winner will become the second team to advance to the Super Bowl with 9 wins, since the league went to a 16-game schedule. Oh, and by the way, the last team to do so, the 1979 Los Angeles Rams, advanced by avenging regular season road losses at Dallas and Tampa Bay. The Rams then played the heavily favored Steelers in the Super Bowl, not in their home stadium, but a few miles away at the Rose Bowl, and had the lead entering the final quarter before the Steelers pulled away late.

Now I won't be so naive as to tell you that familiarity with a stadium is outcome determinative. But I think it's a small, and more importantly, underappreciated part of determining who wins games (or who stays competitive in them). Why is it a factor? Well, it could be related to many different things, all which may come into play. Field surface and conditions could be just one of the factors. Wind patterns (created by unique features of a stadium) could be another. Sound conditions created by each stadium design could be another. Weather patterns and climate is certainly another strong one, where teams from similar playing climates are comfortable and used to playing under the conditions, while those from disparate climates are not. Sun conditions and lighting patterns in the stadium. Heck, the color of the locker room, types of showers. Anything that might be different could come into play, almost imperceptibly, to cause sub-optimal performance.

I've cited three examples where it may have helped some underdogs make history, but let's look at all the info, not just isolated cases. Since 1970, and including last weekend's games, there have been 129 occasions where two teams have played at the same location in both the regular season and post season. I think it's important to further sub-group those games. 56 of those were divisional rematches, and 73 were games between conference opponents. Last January, I also wrote about the playoff bye week and whether it increased home field advantage in the divisional round (concluding it does not). That post also contains data on climate effect in the post season. I think its also important to account for the powerful influence of climate differences on home field advantage in the post season, so I divided those 129 games by whether they were divisional or conference rematches, and by whether the road team had a cold weather climate disadvantage or not.

Type			Season	PF	PA		Playoff PF	PA
DIV-Weather		3-12	20.5	25.3		2-13	14.3	25.6
DIV-No Weather		17-24	19.4	22.2		19-22	18.8	21.4
CONF-Weather		4-15-1	18.2	26.6		6-14	16.9	24.1
CONF-No Weather		9-44	17.0	27.2		15-38	18.6	25.0

And to make it a little clearer, here is a continuation chart showing the average point differentials in both the regular season and playoff games, for each category.

Type			Season PF-PA	Playoff PF-PA	Point Diff. Change
DIV-Weather		-4.8		-11.3		-6.5
DIV-No Weather		-2.8		-2.6		+0.2
CONF-Weather		-8.4		-7.2		+1.2
CONF-No Weather		-10.2		-6.4		+3.8

So let's talk about what is here. When a division opponent with a climate disadvantage gets a second shot, it doesn't really matter. In fact, the climate effect is strong and the drop off is severe. When division rivals meet again, and the teams are either from similar climates or the colder weather team is on the road, there is no change. This makes sense. For these teams, one extra game isn't going to make much difference. They have already played in the stadium continually for several years.

However, we do see improvement in the second game when the opponents are not from the same division. Here, the teams are not accustomed to playing on the same field every season, so the additional chance to return to the same stadium a few months later improves the performance. For the games where the road team is not at a climate disadvantage, the improvement is by close to four points on average. Only three of these conference road rematch teams had a twenty point or more dropoff from the previous result (Denver at Indianapolis, 2004; Minnesota at San Fransisco, 1988; Pittsburgh at Oakland, 1973). In contrast, twelve of the road teams had a twenty point or more improvement over the regular season result.

road	home	year		Reg Season		Playoffs
PIT	IND	2005		L 7-26		W 21-18
LA RAM	TAM	1979		L 6-21		W 9-0
NYG	LA RAM	1984		L 12-33		W 16-13
ARI	CAR	2008		L 23-27		W 33-13
LA RAM	DAL	1979		L 6-30		W 21-19
PIT	DEN	1989		L 7-34		L 23-24
SEA	CHI	2006		L 6-37		L 24-27
NWE  	PIT	2004		L 20-34		W 41-27
DAL	SFO	1981		L 14-45		L 27-28
KAN	HOU	1993		L 0-30		W 28-20
MIN	LA RAM	1977		L 3-35		W 14-7
DAL	LA RAM	1978		L 14-27		W 28-0

I don't think the +3.8 point improvement for these conference road teams is entirely due to the familiarity effect of getting to return to the same stadium. I think there are two other factors at play as well. First, most of these teams lost and performed worse than expected in the first matchup, so there is some natural regression. Dallas, for example, lost by 31 to the San Fransisco 49ers during the regular season, but that result was the anomaly. Second, there is probably also some overconfidence/let down by the home team. After all, they've already beat the team once before at home (often impressively), so they should be able to do it again. Of the nine teams that won the regular season matchup on the road, only three won the playoff rematch (including Baltimore at Miami this year). Thus, twelve of the forty-four losers were able to reverse the results, and ten others lost by a touchdown or less. That said, I do think the familiarity concept is playing a role.

How might all this apply to this weekend's championship games? Well, in the AFC Championship Game, Baltimore and Pittsburgh are similar climate division rivals. As I first discovered in this post, these similar climate rivals (all AFC North games, New England/NY Jets/Buffalo, Chicago/Green Bay, Philadelphia/NY Giants/Washington, San Diego/Oakland, and recently, San Fran/Seattle) show virtually no home field advantage. We've already seen this last week, as the Eagles won at the Giants for the second time in one season. Thus, it should matter very little that this game is being played in Pittsburgh. Pittsburgh is trying to beat Baltimore for a third time, but both games were extremely close and Baltimore had a lead in both late.

In the NFC Championship game, on the other hand, the Eagles will be playing at University of Phoenix Stadium for the first time. Most objective measures would rate the Eagles as the stronger team, and they have already defeated the Cardinals handily. However, the home field advantage that the Cardinals are currently enjoying is an equalizer. I think the Eagles should still win because they are the better team, but IF the Cardinals advance to their first ever Super Bowl, the concept of stadium familiarity will have provided a silent assist.

7 Comments | Posted in Home Field Advantage

Go West! (and then go West again)

Posted by Jason Lisk on October 14, 2008

This season, thanks to the schedule rotation adopted in 2002, both the New England Patriots and New York Jets play four games on the West Coast, against Seattle, San Fransisco, Oakland and San Diego. Until this year, neither has played more than two regular season road games in the Mountain and Pacific Time Zones since the merger. Over the previous four seasons combined, the Patriots have played two regular season games and three post-season games (including last year's Super Bowl in Arizona) out West, while the Jets have played three regular season games and one post-season game.

How rare is it for an Eastern Time Zone team to play this many games out West in a single season? As it turns out, pretty rare. My research has found thirteen individual seasons when an Eastern team has played four or more regular season games out West. For my purposes, I'll define West as both the Pacific and Mountain Time Zones, so I will include Denver and thus not have to figure out if Arizona was or was not on the same time schedule as the California teams due to daylight savings. Before the merger of the AFL and NFL, it was theoretically impossible for an Eastern team to play four games in the West (though we'll find out below it did happen once before). Here are the teams that have travelled West four or more times in a single regular season since the AFL-NFL merger:

1979 Atlanta Falcons (1-3 in West, 6-10 overall) 
1981 Cleveland Browns (1-3 in West, 5-11 overall)
1988 Atlanta Falcons (2-2 in West, 5-11 overall)
1989 New York Giants (3-2 in West, 12-4 overall)
1990 Cincinnati Bengals (2-2 in West, 9-7 overall)*
1991 Atlanta Falcons (3-1 in West, 10-6 overall)
1992 New York Giants (0-4 in West, 6-10 overall)
1994 Atlanta Falcons (1-3 in West, 7-9 overall)
1994 Cincinnati Bengals (1-3 in West, 3-13 overall)
1994 Pittsburgh Steelers (1-3 in West, 12-4 overall)
1997 Atlanta Falcons (2-2 in West, 7-9 overall)
1998 New York Giants (2-2 in West, 8-8 overall)
2005 New York Giants (2-2 in West, 11-5 overall)

*also lost playoff game at Los Angeles Raiders in 1990 divisional round

Two other teams, the 1987 Cleveland Browns, who lost in the AFC Championship game in Denver, and the 1990 New York Giants, who won at San Fransisco in the championship game before winning the Super Bowl, played three regular season games in the West in addition to the fourth game in the conference championship.

It should be no surprise, if you recall that Atlanta played in the NFC West, that they would appear on this list five times. What is surprising is that the New York Giants did it four times, while two other East Coast teams from the same division, the Philadelphia Eagles and Washington Redskins, have never played that many out West.

The sample size of teams here is so low that there is not much meaningful analysis that I can give you as to whether the cumulative effect of this much additional travel in a single season for an East Coast team matters. I went ahead and looked at the simple rating system numbers for each team in the year before and after the extensive Western travelling, compared to the year in question. In the seasons before and after, our Eastern teams had an average SRS of -1.0. In the season in question, the average SRS was -1.3. The Eastern teams performed about -4.0 points worse than their overall SRS in the Western games, which is not that much different from the generally expected 3 points for home field advantage. (I measured this by taking the end of season SRS for the road Eastern team minus the home team, then comparing the actual results versus the expected results from the SRS differences). There was no real pattern to performing worse or better as the season went on, as a whole, as the first game played out West showed the worst score (relative to season SRS) and the fourth game was the second worst.

Of course, New England isn't just playing four games out West. They just concluded back to back games on the West Coast against San Fransisco and San Diego, and stayed at San Jose in between games to practice rather than travel back East. Later this year, they will also play Seattle and Oakland in back to back weeks. This will mark the first time in the history of the NFL that an Eastern team has played consecutive Western games on two separate occasions within the same season.

Extended trips to the West Coast were not unusual for the old AFL teams, the Boston Patriots and the New York Titans/Jets (as well as the Buffalo Bills). In the old AFL, at least prior to Miami and Cincinnati joining, every team played all other league members on a home and home basis. The East Coast teams usually played two, or sometimes even three consecutive games on the road against Oakland, San Diego and Denver. The worst travel start for a team in the history of the AFL/NFL has to belong to the 1967 Boston Patriots, and it was because the team played their home games at Fenway Park. The Patriots opened the season with three consecutive losses on the road at Denver, San Diego, and Oakland. They returned East and won at Buffalo on September 24. The Patriots were scheduled to play their first home game against San Diego. However, the Boston Red Sox won the American League pennant for the first time since 1946, and advanced to play the Saint Louis Cardinals in the World Series. The Patriots lost out to the primary tenants. Even though the Series opened in Boston, and moved to Saint Louis the weekend of October 7th and 8th, the Patriots moved their game with the Chargers back to the West, playing a second game in San Diego. That game ended in a 31-31 tie, which happens to be the last time the Patriots franchise played in a game that ended in a tie.

So how have other teams done when they have played back to back games in the West? I found thirty occasions where an Eastern team has played a game in the West, then returned West to play again a week later (including the post-season). Based on Sunday night's game between the Chargers and Patriots, you might guess it had a big impact. It is a true factual statement (using the SRS differences to account for relative strength of opponents) that those teams collectively performed worse in the second consecutive game on the West Coast than they did in the first, applying the SRS differences for each team in the matchups compared to the actual scores. The Eastern road team was better (relative to their performance in the first game on the road trip) 11 times, worse 18 times, and about the same once.

That said, it's not so much that the Eastern teams played really badly in the second game. It's that they played REALLY well, as a group, in the first. Excluding the New England-San Diego game, since I don't have end of year SRS numbers, the average result in the first game was +0.97 points better than expected, without accounting for home field advantage and the fact the Eastern team was on the road. The average result in the second game was, in contrast, -2.16 worse than expected without accounting for home field, which is not a bad performance for a road team, regardless of where the game is played. I don't see any strong evidence that the performance in the second game was worse than what should be expected for a road team if we had no knowledge of where they played the week before. So New England may be the first team to play back to back games on the West Coast at two different times in the same season, but I don't see any reason to think this is a competitive disadvantage compared to, say, the way the Jets' trips to the West are spaced this season.

10 Comments | Posted in Home Field Advantage

Does the Bye Week Increase Home Field Advantage?

Posted by Jason Lisk on January 7, 2008

There seems to be a generally held belief that teams with byes in the first round of the playoffs have an increased advantage in the semifinals. For example, since 1990, the home teams in the semifinals have won 77.9% of games, compared to 69.1% in the wildcard round, and 58.8% in the championship games. Not only has the winning percentage been higher, there have been more noticeable blowouts in the semifinals than any other round.

The problem with these numbers is that they do not control for matchup. To (try to) answer the question of whether the bye week increases home field advantage, I will use the regular season SRS ratings going back to the AFL-NFL merger, and look at the average expected results, based on regular season ratings, and average actual results in the playoffs for the home team. (I did exclude the two strike seasons of 1982 and 1987, but included every other year from 1970-2006).

7 Comments | Posted in History, Home Field Advantage

Home Field Advantage and Team Efficiency Stats

Posted by Jason Lisk on November 13, 2007

I'm going to take a look at home field advantage, and whether a team's offensive and defensive passing or rushing efficiency stats have any relationship. When I use the term "home field advantage", or "HFA" here, what I really mean is "the difference between the advantage of playing at home, and the disadvantage of playing on the road." But that does not exactly flow off the tongue, so just know that not every thing that creates the difference has to do with the home field or characteristics of the home team.

Also, while the team efficiency stats (which you can find on each team's page as well as the yearly team stats pages) are not perfect, but they are much better than looking at raw yardage numbers. For example, if a team is averaging 4.0 yards a carry, does this mean the team is consistently gaining 4 to 5 yards on a lot of attempts, or that the team is more like a 3.5 yards per carry team, but one with a few big runs boosting the numbers? We cannot answer that as to any particular team, but it is better than nothing. With that in mind, let's look at what team characteristics might be tied to increasing or decreasing home field advantage.

I looked at all teams that finished between 6-10 and 10-6 since Jacksonville and Carolina joined the league (1995-2006). My choice of those records is partially arbitrary-- I could have just as easily narrowed it to 9-7/7-9, or expanded it to 11-5/5-11. But my goal was to look at the middle class of the NFL, teams that generally have some strengths but also some flaws. I felt this dividing line would accomplish that.

For each team, I then looked at the home/road splits in record, and compared it to the team's offensive yards per rush attempt, offensive yards per pass attempt, defensive yards allowed per rush attempt, and defensive yards allowed per pass attempt.

210 total teams finished between 6-10 and 10-6 during the 12 seasons reviewed, an average of over 17 per season--so slightly more than half the teams in the league on average. The entire population averaged 0.586 win percentage at home and 0.417 win percentage on the road, for a +0.169 difference. This would equate to +1.36 more home wins than road wins over the course of a 16 game schedule for the average team.

Two of the categories showed no correlation with changes in home field advantage. These were offensive yards per rush attempt, and defensive yards allowed per pass attempt. Within this population, as both team offensive yards per rush attempt and defensive yards allowed per pass attempt improved, the team's winning percentage, both home and road, improved. However, the differences between home and road stayed fairly constant.

Which leads to the other two categories. Let's start with the stronger of the two, defensive rush yards allowed per attempt. I divided the 210 teams into five roughly equal tiers based on rush defense: excellent (3.6 ypa or lower), above average (3.7 to 3.9), average (4.0 to 4.1), below average (4.2 to 4.4), and poor (4.5 or higher). Here are the home/road splits in winning percentage:

category    no.     home          road          difference
excellent   43      .606          .395          +.211
above avg   50      .614          .403          +.211
average     37      .622          .416          +.206
below avg   41      .537          .419          +.117
poor        39      .548          .460          +.088

It looks like a direct relationship between rush defense and home field advantage, as the better run defenses show an above average home/road difference, while the below average defenses have small splits.

Here are the pass offense numbers, sorted by excellent (7.5 or more ypa), above average (7.1 to 7.4), average (6.7 to 7.0), below average (6.3 to 6.6) and poor (6.2 or lower).

category    no.     home          road          difference
excellent   34      .614          .471          +.143
above avg   36      .608          .429          +.179
average     45      .574          .424          +.150
below avg   50      .578          .396          +.182
poor        35      .568          .382          +.186

These numbers are not nearly as pronounced as the rush defense. There is some tendency for pass offense to be inversely related to home field advantage, as the excellent group is a little below average in home/road difference, and the below average and poor groups perform above average in that respect. However, when we cross-reference rush defense and pass offense, two types of teams emerge that show significant differences in home field advantage.

Fifty-two teams had both an above average or excellent rush defense (3.9 or fewer yards allowed per rush attempt) and a below average or poor pass offense (6.6 or fewer yards per pass attempt). These run stopping, poor passing teams combined to win .604 at home and only .363 on the road, for a difference of +.241. That equates to almost two more home wins than road wins per season on average.

17 of the 52 (32.7%) had at least 3 more home wins than road wins. Only three of these teams finished a season with more road wins than home wins (and all finished with exactly one more road win).

At the opposite end of the spectrum, there were thirty-five teams that finished with a below average or poor rush defense (4.2 or more yards allowed per rush) and an above average or excellent pass offense (7.1 or more yards per pass attempt). These "good passing, can't stop the run" teams won .561 at home and .473 on the road, for a difference of +.088. That is an average of +0.70 more wins at home a season.

Only 6 of the 35 (17.1%) "good passing, can't stop the run" teams won at least 3 more home games than road games. Of these six, three came from Kansas City and Denver, two of the strongest home field advantages in the league. The other three were from dome teams (Detroit 1995, Minnesota 2003, Saint Louis 2004), two of which play in a division with outdoor cold weather rivals.

Almost half of these teams (17 of 35) finished with at least as many road wins as home wins. The 1997 Bengals and 2000 Saints both finished with 4 more road wins than home wins.

If the strength of rush defense does increase home field advantage, there is a potential explanation. If a team is better at stopping the run, it is conceivable that such a team would be somewhat more likely to place its opponent into more 3rd and long situations. This might translate to a bigger advantage at home, where the offense is subject to crowd noise, than on the road, where the home crowd would presumably be quiet to aid the offense. On the other hand, relatively poor passing offense could increase the road disadvantage, for much the same reasons.

5 Comments | Posted in Home Field Advantage

Year Two in a New Stadium

Posted by Jason Lisk on July 2, 2007

Note from Doug: please join me in welcoming JKL to the "staff." He'll be posting articles regularly, or semi-regularly, or whenever he has the time and inclination to bung something down. Glad to have you on board, JKL. [end of Note From Doug]

The Arizona Cardinals have some reasons for optimism entering the 2007 season. Matt Leinart is entering his second year as a starter, with good offensive weapons in the passing game in Anquan Boldin and Larry Fitzgerald. Adrian Wilson is one of the best defensive players in the league. Gone is the coach who was exactly who we thought he was, Dennis Green. Entering is Ken Whisenhunt, who worked under Bill Cowher, and who brings former Steelers offensive line coach Russ Grimm with him.

However, I am not trying to convince you that the Cardinals will be the surprise team of 2007. Predicting a big turn around for the Cardinals is not exactly safe given their history. The Cardinals have been one of the most consistent teams, and it has not been a good consistency. What I will say is that IF the Cardinals turn things around, there will be another factor that could play a role. The Arizona Cardinals will be playing their second season in University of Phoenix Stadium in 2007, after having played the previous 18 years at Sun Devil Stadium in Tempe. If history is an indicator, the Cardinals will enjoy an above average home field advantage in 2007.

Using the very informative site Stadiums of the NFL, I looked at all teams since the AFL-NFL merger who (1) moved to a new stadium, and (2) were playing in the same metropolitan area as the previous season. I found 28 such cases since 1970. Here are the home and road winning percentages for those teams for a 10 year period that includes the two seasons prior to moving into the new stadium, and the eight seasons afterward. Year N represents the first year playing in the new stadium. The first number is the home winning percentage, the second is the road winning percentage, and the third number is the difference between home and road.

  • Year N-2 0.488 0.342 +0.146
  • Year N-1 0.549 0.413 +0.136
  • Year N 0.596 0.404 +0.192
  • Year N+1 0.624 0.397 +0.227
  • Year N+2 0.552 0.408 +0.144
  • Year N+3 0.639 0.454 +0.185
  • Year N+4 0.513 0.463 +0.050
  • Year N+5 0.548 0.477 +0.071
  • Year N+6 0.604 0.399 +0.205
  • Year N+7 0.583 0.417 +0.166

Just so you're reading this correct, Year N+1 is the second year in a new stadium, when the 28 teams won 62.4% of home games and 39.7% of road games for a 22.7% difference, the largest of any year in the period examined. The NFL average home-road difference is going to be closer to 15-17%.

I excluded relocated and expansion teams from this because I wanted to see the effect on home performance, and hoped to minimize the effect of changes in road disadvantage due to a team changing its geographic location and travel schedule, or learning a new league. As we can see, the road performance in Years N-1 (the last year in the old stadium) and N, N+1 and N+2 (the first 3 years in the new stadium) are very similar. The changes were to the home field performance, with an increase in home performance in year 1 of the move, and a further increase in year 2 before beginning to revert back in year 3.

There is a potential explanation for this. It has to do with the familiarity and comfort level of the road team.

From 1986-2005, home teams won 57.2% of divisional games, 58.7% of conference matchups, and 59.8% of inter-conference games. Further, in divisional matchups featuring similar climate rivals from the same time zone, the home team was 340-307 (0.526) for the period 1986-2005. When we look at AFC-NFC matchups between similar climate opponents, where the teams play at each venue less frequently, the home team was 143-101-1 (0.586). (NOTE: Similar climate rivals is defined as teams within 10 degrees of each other's average monthly (Sept. to Dec.) temperature, 72 degrees was used for dome teams, and the monthly average was used for outdoor teams.)

It also makes sense that home field advantage would not be at its strongest immediately upon opening the new stadium, if familiarity plays a role in home field advantage. At the start of year one in a new stadium, the home team is basically no more familiar with the nuances of the new stadium than the visitors. By the start of the year two regular season, the home team will have had at least 12 games experience (preseason and regular season) in the new stadium, while every visiting team will have played 1 or fewer games in the stadium.

Arizona's division rival Seattle presents an interesting recent case study on the potential role of familiarity in home field advantage and road disadvantage. In 2002, Seattle moved in to Qwest Field and changed conferences, moving from the AFC West to the NFC West. In 2003, the Seahawks had a perfect 8-0 record at home, and were 2-6 on the road. When teams traveled to Seattle in 2003, they were almost universally playing in a new situation, as prior to 2000, the Seahawks were a dome team. When Seattle went on the road, they were playing in stadiums they rarely, if ever, had visited in the previous decade. The AFC road opponents that year were Cincinnati and Baltimore, and Seattle had not played a road game in either of those cities since 1997. The conference road opponents were Green Bay, Minnesota, and Washington. Seattle had played at Washington in 2001 and at Green Bay in 1999. Seattle lost all 5 of those road games, and went 2-1 on the road within their new division.

This all leads me to believe that the Cardinals in 2007 will enjoy a better home field advantage. The new stadium alone is not enough to turn a bad team into a playoff team. But if the Cardinals can buck history and improve to an average level, the effects of playing in a new stadium in year 2 could mean the difference between a nice improvement, and a playoff appearance.

8 Comments | Posted in Home Field Advantage

Home field advantage in the playoffs

Posted by Doug on January 3, 2007

Quantifying home field advantage in a particular league can be pretty tricky. Quantifying home field advantage in the postseason is even trickier, at least in the NFL, because the home team is almost always the better team. Since the merger the home team is 214-96 in playoff games, a decisive 69% winning percentage. (I am, of course, only counting the games where there really was a home team. That is, Super Bowls have been excluded.) But how much of that advantage is due to the home field and how much of it is due to the presumably superior quality of the team on that home field?

Prior to the 2002 NFC Championship Game, in which the visiting Tampa Bay Bucs beat the Eagles, I ran some numbers and discovered that in playoff games where the two teams had the same record, the home team enjoyed almost no advantage at all. Since the merger, home teams are just 32-28 in such games. But if the home team has a better record, the advantage seems to magnify very quickly. Here is a chart showing the records of home teams in playoff games against teams whose records were N games worse. For instance, the "1" line indicates that when the home team has a record that is one game better than the road team, the home team is 67-38.

-3 0- 1 0.000
-2 3- 3 0.500
-1 5- 3 0.625
0 32-28 0.533
1 67-38 0.638
2 51-14 0.785
3 29- 4 0.879
4 17- 4 0.810
5 8- 1 0.889
6 2- 0 1.000

Here is the same chart, showing only games since 1993:

-2 1- 1 0.500
-1 2- 1 0.667
0 9-10 0.474
1 33-18 0.647
2 29- 5 0.853
3 10- 2 0.833
4 3- 2 0.600
5 3- 0 1.000
6 1- 0 1.000

The pattern is the same: home teams are only about a 50/50 bet if the teams have the same record or if the home team has a worse record, home teams win about 65% of the time if they are one game better than the visitor, and home teams two or more games better almost never lose (46-9 since 1993). I would have expected the data to be a little smoother than that, maybe 56%, 62%, and 73% or something like that.

Let's compare these numbers to the regular season. I'll look at weeks 13 and 14; that's early enough that almost all teams still have something to play for, but late enough that the at-the-time records have a similar meaning to the records of playoff teams. Here are the results, first for all games since 1970 (compare this table to the first one at the top of the post):

0 60-47 0.561
1 62-35 0.639
2 54-33 0.621
3 44-15 0.746
4 38- 8 0.826

Now for only the games since 1993 (compare this table to the second one):

0 28-25 0.528
1 28-14 0.667
2 26-15 0.634
3 20- 7 0.741
4 20- 3 0.870

The big difference is with teams that have a 2-or-more-game advantage in the records. Based on these data, it appears that the home field doesn't necessarily confer an advantage in the playoffs. Instead, it magnifies whatever advantage is already there. Is this a statistical fluke, or is there something real here? Any theories?

10 Comments | Posted in History, Home Field Advantage

(Travel) time and temperature, part two

Posted by Doug on October 3, 2006

This is a continuation of yesterday's guest column by JKL:

Today, I am going to look at the effect of climate. This study is a little less exact than calculating the distance between two cities. After all, most cities are not like Rock Ridge; they do not change locations overnight. However, temperatures can and do fluctuate throughout a season. It would be too time consuming, and probably impossible, to find accurate weather information on every divisional game played from 1986-2005, so I tried to do the next best thing.

To get a general sense of the effect of climate, I used the National Weather Service median daily high temperatures for each city from the months of September through December, and averaged those 4 months. For teams that played in a dome, I approximated 74 degrees as the average in-season temperature. Houston, because of the retractable roof, was a potential problem, but as it turns out, the average in-season daily high in Houston (if you consider Houston an outdoor team) is only 2 degrees higher than my guess at dome temperatures.

The list below is similar to the distance list from yesterday. It lists the home team wins and losses in divisional series between 1986-2005, sorted by the average in season temperature difference (in Fahrenheit) between the two cities.

temp diff Home W Home L Home T Pct
0 to 5.0 348 305 2 0.533
5.1 to 10.0 303 258 0 0.540
10.1 to 15.0 161 103 0 0.610
15.1 to 20.0 170 109 0 0.609
20.1 to 25.0 132 81 0 0.620
25.1 plus 124 75 0 0.623

Now, let's cross-reference both distance and climate differences, and see what we get.

temp diff 0-400 401-800 801-1200 1201-1600 1601+
0 to 5.0 0.528 0.561 0.526 0.450
5.1 to 10.0 0.515 0.455 0.552 0.613 0.605
10.1 to 15.0 0.517 0.646 0.631
15.1 to 20.0 0.646 0.574 0.531 0.652 0.667
20.1 to 25.0 0.660 0.625 0.571
25.1 plus 0.650 0.608 0.600

This seems to show that both distance and climate matter. At distances less than 800 miles, so long as the temperature difference is not extreme, the home field advantage is very small. Conversely, at longer distances, so long as the playing environments are very similar, the home field advantage is very small. Divisional opponents from similar playing climates, but at distances beyond 800 miles, have a home record of only 65-64-2. Consider the farthest single divisional matchup in terms of distance, San Fransisco versus Carolina in the pre-2002 NFC West. Despite the change of three time zones and over 2300 miles, the two cities have almost identical in-season average temperatures, and the road team won 8 of 14 games.

However, at longer travel distances, once the cities/playing environments start to deviate in temperature beyond five degrees difference, the home field advantage does kick in and increase dramatically.

To demonstrate the strong effect of playing climate change, here is a look at the home team records in series between the current NFC North teams, since 1961. In 1961, Minnesota joined the NFL, and the 4 teams have been divisional rivals since that year. Following the 1974 season, Detroit moved from Tigers Stadium to the Silverdome. Following the 1981 season, Minnesota moved from Metropolitan Stadium to the Metrodome. The Bears and Packers have played outside, as the Good Lord and Lombardi intended it, the entire time.

team 1 team 2 years Home W Home L Home T Home Pct
Chicago Detroit 1961-1974 13 14 1 0.482
Chicago Detroit 1975-2005 40 21 0 0.656
Chicago Green Bay 1961-2005 45 43 0 0.511
Chicago Minnesota 1961-1981 22 18 2 0.548
Chicago Minnesota 1982-2005 28 19 0 0.596
Detroit Green Bay 1961-1974 11 12 5 0.482
Detroit Green Bay 1975-2005 41 21 0 0.661
Detroit Minnesota 1961-1974 11 15 2 0.429
Detroit Minnesota 1975-1981 11 3 0 0.786
Detroit Minnesota 1982-2005 26 21 0 0.553
Green Bay Minnesota 1961-1981 17 24 1 0.417
Green Bay Minnesota 1982-2005 29 18 0 0.617
Outdoor Outdoor 1961-2005 119 126 11 0.486
Outdoor Dome 1975-2005 149 82 0 0.645
Dome Dome 1982-2005 26 21 0 0.553

Note that the home team is only 119-126-11 when the two teams both played their home games outdoors. Granted, during some of those years, there has been a significant power difference between the haves (Green Bay of the 60s, Minnesota of the 70s, Chicago of the mid-80s) and the have-nots (Detroit, and with condolences to MDS, pick your decade). However, when upsets have occurred, they have been more likely to occur on the better teams home field. Consider 1966 and 1967. Green Bay went on to win the Super Bowl both years, but lost to a rather poor Minnesota team at home (while winning in Minnesota) both seasons.

If you asked most NFL announcers what the biggest factor in creating home field advantage was, most would probably attribute a large part of it to crowd noise. This research casts some doubt on that view. I am guessing that the crowd is no less loud (and probably is louder) in divisional rivalry games against close geographic neighbors, such Bears-Packers, Steelers-Browns, or Eagles-Giants. Despite "crowd noise" in these games where the teams are in close proximity and play their home games in similar environments, the home field advantage has been, and continues to be so far in 2005 extremely small.

11 Comments | Posted in Home Field Advantage

(Travel) time and temperature, part one

Posted by Doug on October 2, 2006

Longtime readers of this blog know that a guy with the handle JKL always has interesting things to say in the comments. In particular, he did a couple of very interesting home field advantage studies awhile back. I asked him if he'd be willing to write those up and let me post them here. He agreed, and so I'll be posting them today and tomorrow. Thanks JKL!

Kansas City and Denver are generally considered to have two of the best home field advantages in the NFL. More often than not, this is attributed to, in Denver's case, the altitude, and in Kansas City's case, the environment ("crowd noise") at Arrowhead Stadium.

But is there another explanation? Denver and Kansas City are more geographically isolated from their conference opponents than any other franchises in the NFL. In fact, they are each other's closest geographic neighbors, separated by approximately 567 miles and 4,000 feet in elevation change. Denver's next closest AFC opponent is division rival San Diego. Kansas City's next closest is non-divisional Indianapolis. Compare this to Pittsburgh, who is within 300 miles of all 3 divisional opponents, and within 500 miles of several conference opponents (Buffalo, Tennessee, New England, New York Jets, Indianapolis).

To examine this more closely, I looked at all divisional series played between 1986-2005. With a few exceptions from the 1987 strike season, all divisional series have been played on a home and away basis over that span. This method was chosen because it allows us to compare 2 games, at different sites, each year, to see which series feature a high percentage of home team splits, compared to those that feature more sweeps or series splits where the road team wins both times. Obviously, if a Super Bowl contender is playing a first overall pick contender (like Indianapolis and Houston last year) it is going to make little difference where the game is played. The hope is that over the course of 20 seasons, things will even out, and the series will show roughly even distribution of years where the teams were relatively close, and those were one team was significantly better than the other. I was not concerned about which specific team in the series was winning more, but rather, how often the home team in the series won.

I then looked up the geographic straight-line difference (in miles) between each city in a series (as opposed to the driving distance) because I wanted to get a good approximation of travel time by air on a charter plane. With the exception of Green Bay playing down the road in Milwaukee, I excluded those years when one team played its games in two or more cities, such as New Orleans of 2005. Below are the winning percentages of the home team in divisional series, sorted by geographic mileage between the two cities.

Distance W L T PCT
within 400 363 293 0 0.553
401-800 248 205 0 0.547
801-1200 332 235 1 0.585
1201-1600 172 102 0 0.628
1601-2000 56 42 0 0.571
2001 or more 74 55 1 0.573

Conventional wisdom is that distance matters at extreme distances such as cross-country trips. However, the series beyond 1600 miles, which consist of pre-2002 series involving Arizona in the NFC East, and San Fransisco and Los Angeles versus the other old NFC West opponents, show no greater home field advantage than those at, say, 1100 miles difference.

For some concrete examples of the effect of short distances, here are the divisional series that have been played between 1986-2005 where the teams are within 300 miles, with the miles separating the teams, followed by the home team's won-loss record:

team 1 team 2 distance (mi) Home W Home L
nyg phi 90 22 18
rai (la) sdg 108 7 11
cle pit 125 19 15
phi was 133 23 17
chi gnb 167 17 23
rav (bal) pit 198 11 9
cin cle 210 19 15
nyg was 219 21 18
atl car 228 15 7
cin oti (ten) 245 5 5
chi det 247 26 13
cin pit 253 19 21
clt (ind) oti (ten) 260 4 4
gnb min 266 26 14
det gnb 283 26 14

Notice the winning percentages in the series involving one dome team against an outdoor team, versus those involving two outdoor teams. In Outdoor only series, the home team was 181-174, a paltry 51.0%. In series involving a dome team, the home team was 97-52 (65.1%). Basically, in outdoor series where the teams were relatively close geographically, the home team has had virtually no home field advantage. This has been borne out again this season, as New England won at New York Jets, Cincinnati won at Pittsburgh, Chicago won at Green Bay, and the New York Giants won at Philadelphia. Does this mean the road victor is going to cruise to victory at home later in the year in these series, because they already won on the road? If history is any indicator, the answer is no.

It also raises the interesting question of climate, and how much of what is showing in this distance data is actually due to climate differences, rather than the effect of travel time. Most of the dome series results are from the current NFC North teams, where the difference in playing temperature between playing outdoors and playing in a dome can be very significant.

Tomorrow, I will look at climate differences, and also put the old Black and Blue Division under the microscope. The NFC North teams provide a good case study because not only are two teams outdoor cold weather teams, and two teams indoor controlled weather teams, but because all four teams used to play outdoors. Thus, we can see the effect that changing to domes has had on home field advantage in those series.

9 Comments | Posted in Home Field Advantage

Home Field Advantage II

Posted by Chase Stuart on July 13, 2006

Is there such a thing as a "dome field advantage?" Whenever a dome team has a strong season and happens to be very good at home, sportswriters get to write about the special dome field advantage. Supposedly, it's tougher to win in a dome because of the loud crowd noise, and maybe the artificial turf and the absence of natural elements. So do the facts bear this our? Do dome teams do better than regular teams at home?

According to the data, the answer is no. That's an important caveat, though. The numbers just show one thing: home wins minus road wins, for all teams that played in a dome. It's certainly possible that some special advantage exists for dome teams that wasn't examined in this study. But at the end of this post I'll throw out a theory on why there might actually be a "dome team disadvantage."

Since 1983, eight teams have played in a dome. The Atlanta Falcons (1992-2005), Detroit Lions (1983-2005), Houston Oilers (1983-1996), Indianapolis Colts (1984-2005), Minnesota Vikings (1983-2005), New Orleans Saints (1983-2004), Seattle Seahawks (1983-1999) and the St. Louis Rams (1996-2005).

There was a bit of noise in the data, so I eliminated the '95 Rams and last year's Saints teams. When the Rams relocated to St. Louis in 1995, the Edward Jones Dome wasn't complete. So the Rams first four home games were played at Busch Stadium, and the remainder in the Dome. The Rams went 3-1 at Busch and 1-3 indoors. Due to Hurricane Katrina, the Saints played three games indoors at the Alamodome in San Antonio (1-2), and four home games outdoors at Tiger Stadium in Baton Rouge (0-4) last year. The remaining "home" game was played at Giants Stadium, the star of yesterday's post.

The eight dome teams won 188 games more at home than on the road during the relevant time period, spanning 139 seasons. That comes out to an average of 1.35 more home wins per season.

The Houston Texans (2002-2005) play in Reliant Stadium, which has a retractable roof. I'm not sure which games were played with the roof open and which with the roof closed. The Dallas Cowboys (1983-2005) play at Texas Stadium, which is an open-air stadium -- basically a dome with a hole in the center. I didn't know whether to count either Texas team as a "dome" team or "regular" team, so I just put them in a separate category. Interestingly enough, my classification shouldn't matter: over 26 seasons the two teams won 35 more home games than road games, an average of 1.35 more wins per season.

So how does that compare to the rest of the NFL? The league has increased from 28 to 32 teams since the first year in the study. Over the 22 seasons (remember, the 1987 strike season data were excluded), that amounts to 649 seasons. NFL franchises have won 881 more games at home than on the road, average of 1.36 more wins per season. If you eliminate all the dome teams, the Cowboys and Texans, and the 2005 Saints and 1995 Rams, NFL teams average 1.37 more wins per season at home than on the road.

We have 482 non-dome seasons, and 188 dome seasons. I'm not sure what a "significant" sample size would be, but considering how close the two averages were (1.35 and 1.37), at the least the burden of proof should shift to those who think dome teams have an advantage.

I promised you some theory in addition to the numbers. We've seen that dome teams appear to have the exact same home field advantage as regular teams. I say appear, because all the data show is that dome teams win the same additional number of games (compared to regular teams) at home than on the road. But is it possible that dome teams are actually worse at home but the numbers don't show it?

Isn't the general feeling that dome teams aren't as good on the road because they're not used to the conditions? This would artificially inflate a dome team's rating under my current system, because a team grades better at home the worse it does on the road. If dome teams actually perform poorly on the road -- as we might expect -- then the HFA of dome teams should should be greater than the league average, if dome teams are equally strong at home. This leads us to one of three conclusions:

  • Dome teams are actually weaker at home; they just look equal because they have trouble winning on the road.
  • Dome teams actually aren't weaker at all on the road; it just seems that way because we hear it all the time. The flipside of all the above numbers is that dome teams only lose 1.35 less games on the road than at home each year.
  • Something else. Maybe it's a small sample size. Maybe dome teams are below average at home when they're bad, but above average at home when they're good. Maybe schedule somehow factors in here. Maybe there's some other force driving the numbers that I haven't isolated. Who knows.

There's also the argument that dome teams are still actually better at home, but the numbers don't show it. Let's take a quick look at a few case studies. We'll use HFA rating as a shorthand for home wins minus road wins.

Atlanta's HFA rating was 9.5 during the 8 years the Falcons played at Fulton County Stadium; playing indoors the last 14 seasons, Atlanta's won 22.5 more games at home. The Houston Oilers' HFA was 21 in thirteen seasons at the Astrodome; the Titan's HFA rating was 9 in 9 years. But on the other hand, the Seahawks won just 23 more home games than road games in sixteen seasons in the Kingdome. Since moving to Qwest Field, Seattle's HFA is 12 in six years.

Here's an interesting one. From 1983-1994, the Raiders and Rams both won 9 more games when playing in Los Angeles than when on the road. The Raiders moved to Oakland and despite the notoriety of Raider Nation and the Black Hole, have an HFA of only 11 in 11 years. The Rams, in ten season indoors, won 15 more at home.

If there's such a thing as a Dome Field Advantage, it's certainly hard to quantify it. My guess is that when teams like the '98 Vikings, '99 Rams or the '05 Colts have a dominant offense and look unstoppable at home, it's a nice story to think it's the dome that helps. But in general, great teams almost always look pretty good, and usually look unbeatable at home no matter where they play. The same people that talk up how hard it is to play against a dome team because of the noise, probably mention how difficult it is to win in the cold against the Packers, Broncos and Chiefs. Even teams with no special weather advantage -- warm weather teams like Arizona, Tampa Bay and Dallas -- have above average HFA factors.

We know that over the last 22 years, home teams have won 58.5% of all games. I'll end with a breakdown of HFA separated out by total team wins.

Wins	HFA	Teams	HFA/Teams
1 -4 6 -0.67
2 12 14 0.86
3 29 25 1.16
4 48 44 1.09
5 76 54 1.41
6 94 60 1.57
7 79 69 1.14
8 112 70 1.60
9 121 77 1.57
10 94 73 1.29
11 79 55 1.44
12 66 43 1.53
13 46 22 2.09
14 4 15 0.27
15 2 4 0.50

3.5 -1.5 1 -1.50
4.5 5.5 3 1.83
5.5 -0.5 1 -0.50
6.5 9.5 3 3.17
7.5 -2.5 1 -2.50
8.5 7 4 1.75
9.5 2 2 1.00
10.5 3.5 3 1.17
Totals 881 649 1.36

7 Comments | Posted in Home Field Advantage

Home Field Advantage

Posted by Chase Stuart on July 12, 2006

In 2009, the Jets and Giants will move into a new joint stadium. It probably will be named after some corporation (JetBlue?), which is a big change from where both teams currently play: Giants Stadium. Jets fans don't like that their team plays in a stadium named after another team, and have claimed for years that it's negatively impacted the team's success. Giants fans, of course, think their stadium gives the team a great home field advantage.

While we don't know whether the name of where the Giants play home games will negatively affect New York's success, we have all the data we need to examine how Giants Stadium has been to the Jets and the Giants. That wouldn't make for much of a blog post though, so let's take a look at home field advantage throughout the entire NFL.

The Jets moved into Giants Stadium in 1983. So have the Jets really been harmed by being "homeless"? Measuring home field advantage may not be easy, but I think a team's home wins minus a team's road wins is a pretty accurate metric. Last year, Denver went 8-0 at home and 5-3 on the road, for example. Cincinnati went 5-3 at home, and 6-2 on the road. Ignoring the small sample size, that's strong evidence that the Broncos are a better home team than the Bengals.

If you just look at a franchise's winning percentage at home, you're going to overvalue the good teams. By subtracting a team's road wins from its home wins, you should get a strong idea of how good that team is at home (more on this and the NFC North at the end of this post).

So how do the Jets fair? Over the past six years, the Jets and Giants have the same number of home wins (27), while the Giants (23) have two more road wins than the Jets. This doesn't prove anything of course, but it's safe to say that the Jets and Giants were pretty equivalent in terms of football ability from 2000-2005. And while both teams won 27 games at home, it's arguable that the Jets actually enjoyed the better home field advantage since Gang Green was the worse team (based on the overall records).

Of course, I soon realized that six years wasn't enough. But this gives us a glimpse of two key ideas: home field advantage isn't consistent from year to year, and you should always be careful with your sample sizes. As Doug showed here we should always be careful with splits.

If you look at the last four seasons, the Jets have won nine more home games than road games; the Giants just three. If we go back ten years, the Jets have won 8 more at home than away, Big Blue won 8.5 more. So whatever cutoff you use may seem arbitrary and a different cutoff could very well get you a different result.

But let's use 1983, when the Jets left Shea Stadium. Because so many NFL teams have changed cities, this list of full of caveats, most of which are in the footnotes. I didn't put footnotes next to Jacksonville (1995-2005), Carolina (1995-2005) and Cleveland (1983-1995; 1999-2005), but you should note that those data are not from a full 22 seasons. One other note: I didn't include any data from the strike season of 1987.

HFA is the Home Field Advantage factor, which is simply total home wins minus total road wins. Ties were counted as half a win.

Team HFA

Kansas City 56
Denver 52
Detroit 41.5
Green Bay 40
Minnesota 39
Cincinnati 37
Tampa Bay 37
Buffalo 37
Chicago 35
Seattle 35
Pittsburgh 33.5
Dallas 33
Atlanta 32
Miami 31
Arizona1 28
New England 26
Washington 25.5
San Diego 24
Baltimore2 22.5
New York (N) 22
Houston3 21
San Francisco 20.5
Philadelphia 20.5
Indianapolis4 19
St. Louis5 16
Jacksonville 16
Cleveland 12.5
Oakland6 11
New York (A) 10.5
Tennessee7 9
LA Raiders8 9
LA Rams9 8
Carolina 8
New Orleans 6
St. Louis10 6
Houston11 2
Baltimore12 -1

1 Arizona (1994-2005) and Phoenix (1988-1993) Cardinals. For the St. Louis Cardinals, see footnote 10.
2 Baltimore Ravens (1996-2005). For the Baltimore Colts, see footnote 12.
3 Houston Oilers (1983-1996). For the Tennessee Titans see footnote 7; the Houston Texans, footnote 11.
4 Indianapolis Colts (1984-2005). For the Baltimore Colts, see footnote 12.
5 St. Louis Rams (1995-2005). For the Los Angeles Rams see footnote 8.
6 Oakland Raiders (1995-2005). For the Los Angeles Raiders see footnote 9.
7 Tennessee Titans (1997-2005)
8 Los Angeles Rams (1983-1994)
9 Los Angeles Raiders (1983-1994)
10 St. Louis Cardinals (1983-1986)
11 Houston Texans (2002-2005)
12 Baltimore Colts (1983)

I'll let you guys comment on the list, but there's one more thing to mention. The old NFC Central (1983-2001) and current NFC North is very well represented on this list: three teams in the top five, and two more in the top ten (of course Tampa Bay's in the NFC South these days).

There's probably a good bit of synergy on this list. If Green Bay is dominant at home and bad on the road, when Minnesota plays Green Bay, the Vikings will probably lose at Lambeau Field but win at home. That will artificially inflate the Vikings HFA factor. If all the NFC North teams have strong home field advantages -- and most fans probably think the Bears and Packers do -- that will drive all the NFC North teams up this list. The Bucs are an interesting study too. Tampa ranked in the top five in HFA factor from 1983-2001, with 34 more home wins than road wins. That's an average of 1.89 wins more per year playing at home. Since joining the NFC South, the Bucs have won only three more games in four years at home.

21 Comments | Posted in Home Field Advantage

More home cookin’

Posted by Doug on May 22, 2006

Last week I posted this breakdown of success rates at home versus on the road on third (or fourth) and one when the play was close. I'm just going to throw out a few similar breakdowns here. As I said in the previous post, I don't think it's possible to determine from the stats whether there is an officiating-related home field advantage, so I'm going to refrain from commenting much. I just thought you might be interested in the numbers.

First, here is the dual breakdown to the one I presented last week. The first column is the exact data I presented in the last post. The second column contains the conversion rates on plays that were not close (and hence where a spot couldn't have made a difference).

Success rates on rushing plays on (3rd-or-4th)-and-1

When the play is close When not close
home team 48.7% 87.2%
road team 40.8% 86.7%

And here is some further detail:

All (3rd-or-4th)-and-1 rushing attempts

Gain<0 Gain=0 Gain=1 Gain>1
home team 8.3% 17.7% 16.9% 57.0%
road team 8.2% 22.8% 15.7% 53.3%

Finally, these data should give us an idea of what the overall home field advantage is on 3rd down (and 4th down) plays.

Success rates on all (3rd-or-4th)-and-N plays

N Home Road
1 68.6% 66.0%
2 53.3% 51.2%
3 52.7% 53.0%
4 48.1% 47.3%
5 42.6% 40.4%
6 44.9% 40.8%
7 36.2% 39.0%
8 32.1% 31.5%
9 33.2% 29.2%
10+ 21.0% 19.2%

3 Comments | Posted in Home Field Advantage

Home cookin?

Posted by Doug on May 19, 2006

You know what I hate?

The quarterback sneak.

I acknowledge that it's generally a pretty effective play if you need to pick up two inches. But it's really ugly. And besides that, it puts the refs in a tough spot. On most quarterback sneaks, it's impossible to get a decent spot because no one --- not the refs, the fans, or even the TV cameras --- can see through the pile of bodies well enough to pinpoint the exact spot of the ball (which you can't see) at the time that the knee (which you can't see) touches the ground (which you can't see) or figure out when the forward momentum of the ball carrier was stopped. It just can't be done. And the result is that the ref has to arbitrarily decide whether to award a first down or not.

That makes me wonder whether the arbitrary spots that the home team gets might be different from the arbitrary spots that the road team gets. I decided to take a very incomplete preliminary look at some data to see if anything interesting would turn up. And, though I started this post talking about quarterback sneaks, I'm going to open up the data to the broader topic of short-yardage situations.

So here is what I did. I looked at all 3rd-and-1 and 4th-and-1 situations during the past three seasons in which a rush was attempted and where the rush gained either zero or one yard. Inasmuch as we can tell from the play-by-play data, those would be the plays where a spot could make the difference. Here is the data:

attempts successes success rate
home team 357 174 48.7%
road team 390 159 40.8%
TOTAL 747 333 44.6%

Given the sample sizes involved, it's very unlikely that such a split would happen by chance if the true success rates were equal. So we have pretty good evidence that the success rates are not the same. It's pretty likely that something is going on here.

I need to state clearly that this does not necessarily say anything about the refs and whether their spotting guesses are influenced by the home crowd. The refs are just one of many possibilities for the something that is going on. Teams in all sports do all sorts of things better at home than on the road, so this could be just another non-officiating-related manifestation of that slippery character named home field advantage.

Or maybe it's not. This data isn't merely saying that the home team converts more often on 3rd-and-1. It's saying that they convert more often on 3rd-and-1 when the play is close. I don't think it's possible to statistically separate the officiating-related home field advantage (if any) from the non-officiated-related home field advantage, so we'll never know. But this looks a bit suspicious to my paranoid eye.

I think sports rooting is a good outlet for me to release all my irrationality. Most people who know me consider me pretty logical and level-headed, and generally I am. As I sit here typing this, I truly believe that "this does not necessarily say anything about the refs and whether their spotting guesses are influenced by the home crowd. The refs are just one of many possibilities for the something that is going on." But the first time a team I'm rooting for gets a bad spot on the road, this data will become iron-clad evidence of widespread conspiracy.

That's healthy, right?

10 Comments | Posted in Home Field Advantage