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Why 13>14, how Devin Hester cost the Bears Super Bowl XLI, and other mysteries

Posted by Doug on October 9, 2008

For reasons unknown to me, my referrals logs last week showed several clicks from this Phil Birnbaum post about this nearly-two-year-old Chase Stuart post about the odd fact that NFL teams win more often when they score 13 points than when they score 14.

It turns out that, in the aggregate, teams allow fewer points when they score 13 than when they score 14.

Commenter Alex said this:

It’s not that scoring two field goals instead of a touchdown causes a team to win, it’s that being in the lead causes a team to score two field goals instead of a touchdown.

To which I added this:

It didn’t occur to me, but now that you phrase it that way, it’s just another version of the old “Dallas is 97-2 when Emmitt rushes the ball 30 or more times” schtick.

Nobody runs the ball when they’re trailing big, and nobody kicks field goals when they’re trailing big.

Now that we've got detailed scoring logs, I can investigate this a little further. Consider this:

Since 1970, teams that score their 13th point in the second half find themselves either tied or in the lead 58% of the time after scoring that 13th point.

Teams that score their 14th point in the second half find themselves either tied or in the lead only 48% of the time after scoring that 14th point.

In the fourth quarter, those numbers are 52% and 35%.

[Obviously, I'm ignoring the brief instant between a TD and a successful PAT in both calculations.]

Or consider this:

A second-half field goal either ties the game or gives the team the lead 75% of the time. A second-half TD either ties the game or gives the team the lead only 69% of the time. That's a slim margin, but it's real; these are huge sample sizes. In the fourth quarter, those figures are 81% and 66%.

I think this is pretty solid evidence that scoring 13 points is an effect, rather than a cause, of winning games.

While I was wading around in the database, I scraped up a few other fun facts.

Here's another one from the correlation-is-not-causation file...

Since 1978, teams that have a kickoff return for a touchdown win 52% of the time, but teams that have a punt return for a touchdown win 69% of the time. Teams that have an interception return for a touchdown win 76% of the time. Teams that have a fourth-quarter interception return TD win 90% of the time.

Why? Because teams that are returning kickoffs are teams that were just scored upon (usually), while teams that are returning punts are teams that just played some good defense. Passes that turn into interception return TDs are often either (1) risky passes or (2) passes thrown by poor quarterbacks or into very good secondaries. Risky passes --- especially in the fourth quarter --- are far more likely to be thrown by teams that were already losing. Teams with bad quarterbacks are also more likely to be losing. So it's not that pick-sixes are worth more than kick returns; it's just that they happen to teams that are richer.

Now here's one that I don't understand...

Since 1950, there have been 75 opening kickoffs returned for TDs. Only 46.8% 53% of those teams won the game. Contrast that with the 63% win percentage for teams who score a 1st quarter non-kickoff-return TD to take a 6-0, 7-0, or 8-0 lead.

EDIT: I originally erroneously posted 47%, but I was reading it backwards. 53% is the correct number.

When I presented this to Chase, he pointed out that an opening kickoff return TD is worth about 5.7 points (prior to the kick the receiving team has about a 0.7-point expectation, the TD is worth 6.4, so the net is 5.7). So if the two teams were equally matched, Chase reasons, an opening kickoff return score essentially makes the scoring team a 5.5- or 6-point favorite, and those kinds of teams win 70--75% of the time. So why did these teams win only 47% 53% of the time?

My first thought was that these 75 particular teams might have just happened to be weak teams. This might be the result of random chance, or it might be due to a general tendency for weaker teams to have stronger kick return units (I have no idea if that tendency exists, but it is plausible: weaker teams have more incentive to have good kick return units, and they get more practice!). But as far as I can tell, that wasn't the case. These 75 teams had an overall winning percentage, in all games, of 49.5%.

Maybe a game-by-game look at all 75 games would reveal something, but before I do that I'll open the question to you:

Does returning the opening kickoff for a TD hurt your chances of winning?

I don't think so, but I can't find the easy explanation for this phenomenon.

EDIT: even after the correction, it's still an interesting bit of data, but quite a bit less mysterious. It is almost certainly due to random chance, plus a collection of factors mentioned in the comments.

This entry was posted on Thursday, October 9th, 2008 at 5:04 am and is filed under General. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.