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.

Does the decision to share a stadium (again) have a potential effect on the home field advantage that the two New York franchises will have in the New Meadowlands? Let's start by looking at the home field advantage rankings of every franchise since 1984, when the Jets and Giants began sharing the Meadowlands, by looking at the difference between home and road winning percentage. These are updated through the end of the 2008 season and include regular season only.

rank    team     home    away     diff.
=======================================================
1	kan	0.668	0.380	+0.288
2	den	0.745	0.475	+0.270
3	rav	0.649	0.385	+0.264
4	min	0.655	0.422	+0.233
5	tam	0.533	0.305	+0.228
6	crd	0.477	0.263	+0.215
7	htx	0.464	0.250	+0.214
8	pit	0.686	0.475	+0.211
9	sea	0.610	0.402	+0.208
10	det	0.480	0.275	+0.205
11	buf	0.600	0.397	+0.203
12	cin	0.498	0.302	+0.196
13	gnb	0.638	0.447	+0.190
14	chi	0.630	0.447	+0.183
15	jax	0.616	0.438	+0.179
16	atl	0.503	0.324	+0.178
17	dal	0.608	0.440	+0.168
18	mia	0.638	0.480	+0.158
19	oti	0.608	0.455	+0.153
20	sdg	0.538	0.390	+0.148
21	was	0.590	0.445	+0.145
22	sfo	0.678	0.553	+0.126
23	phi	0.613	0.490	+0.123
24	ram	0.523	0.410	+0.113
25	new	0.615	0.503	+0.112
26	rai	0.530	0.422	+0.108
27	nyg	0.615	0.510	+0.105
28	clt	0.565	0.462	+0.103
29	nyj	0.498	0.417	+0.080
29	car	0.527	0.446	+0.080
31	cle	0.454	0.386	+0.068
32	nor	0.492	0.465	+0.027
=======================================================

The Giants and Jets both finish in the bottom 6 in home/road differential since 1984, with the Giants at 27th and the Jets tied for 29th (out of 32 teams). But those numbers are for the overall period, now let's break that down into five year blocks to see what the combined home/road splits have been for the two franchises since 1984.

Five year records, Giants and Jets combined, since 1984

		Home Pct	Away Pct	Difference
========================================================
1984-1988		0.681	0.474	+0.207
1989-1993		0.538	0.463	+0.075
1994-1998		0.488	0.381	+0.106
1999-2003		0.513	0.513	+0.000
2004-2008		0.568	0.481	+0.087
========================================================

The Giants were +0.122 in home/road differential from 1976-1983, prior to the Jets moving in to the stadium. We see that since 1989 (the sixth year after sharing a stadium), the home field advantage for the two franchises has been even lower (+0.067 home/road differential).

Now, why could road team familiarity play a role in reducing the Giants' and Jets' home field advantage? Because teams play there more frequently than other venues. Once the Lions play at the Giants later this year, every team will have played in the Meadowlands at least once (and often times more than once) in the last five years.

The home field advantage in interconference matchups has typically been higher than other matchups. However, when interconference road teams visit the New York teams, they are not visiting a place they see only once a decade. We should see reduced home field advantage, particularly in games against the other New York team's division rivals, who already play there once a year.

And that is exactly what we see in the games where the Giants and Jets play the AFC/NFC East in interconference matchups at home. New York Teams are only 5-15 at home against all other AFC/NFC East in interconference matchups since 1984. The specific matchups dictate some of that record, but even accounting for relative team strength, the New York teams have very little home field advantage in these games. For comparison, in all other AFC East versus NFC East matchups (other than those played at the Meadowlands), the home team is 67-49 (.577).

So how much does sharing a stadium impact the home field advantage? I don't think you can just look at the average home field advantage league-wide. The New York teams have other factors at play, besides sharing a stadium, that should reduce home field advantage. They play in divisions with close proximity rivals who also play outdoors. They have a lot of other opponents near them geographically as well. If the Giants played in a division with the Buccaneers, Saints and Falcons, I would expect them to show a higher home/road differential. We also don't know how strong the Giants' home field advantage would have been if the Jets had moved into a different stadium back in 1984. We can, however, make some educated estimates. The three division opponents that are within 200 miles of the Meadowlands (Patriots, Redskins, and Eagles) do all show below average home/road splits at +0.127 combined. The Giants, in the eight years before the Jets moved in, had a similar split, at +0.122. Using an estimate of +0.125, and comparing that to the home/road splits over the last twenty years at the Meadowlands, results in a difference of 0.058 per year. Multiplying that by 8 home games equals about 0.46 home wins per year per team.

I want to expressly state that I am not taking a position on whether the Giants or Jets should have continued their relationship into a new stadium, or whether the Raiders and 49ers should also consider such a possibility. Financial and political considerations obviously play a big role in both cases. I am just pointing out that a team may derive some competitive advantage from not sharing a stadium, which of course may be more than counterbalanced by all the other considerations (getting a better stadium with more amenities and more income by having a shared arrangement, or even getting a stadium at all).

As for Eli, I don't think it has anything to do with him or any one individual player. I don't think he started a single game in the Meadowlands from 1999-2003, when the two New York teams combined to win as many on the road as at home. I fully expect the two New York teams to experience a marked increase in home field advantage in the first few years in the new stadium, and for that to dissipate over time. In a few years, I expect that we will hear how Eli and the Giants do so much better at home than they used to.