Sunday, February 28, 2010

Overtime Omnibus

Lately, every time PFT has a post complaining about OT rules, I think of something else to look at regarding OT games.

Here's some more OT-related stats.

Overtime margin of victory, regular season and playoffs

This is somewhat of an overlap on what I've previously posted, but I want to have the complete stats for regulation and playoffs in one place.

This is for all 445 regular-season overtime games (going back to the 1974 season), and all 27 playoff overtime games (going back to the first one, in 1958).

Margin  Reg. Season%  Playoffs%
3312 70.1%19 70.4%

The two overtime games won on a safety are here and here.

Last team to score in regulation

Back on my first post on OT rules, I suggested there is a correlation between OT winners and the last team to score in the regulation period. It turns out there is, though it's much stronger in playoff games than in the regular season.

Of the 27 playoff overtime games (the lst 24 listed here), 18 (66.7%) were won by the same team that scored last in regulation.

Of the 445 regular season overtime games, the last team to score in regulation was 224-204-17 (52.2%, counting ties as a half-win, which may or may not make any sense in this context). Not as marked as the playoffs, but still an advantage.

Home field advantage in overtime

In the playoffs, 15 of the 27 overtime games (55.6%) were won by the home teams, and 9 (44.4%) were won by the visiting teams.

In the regular seasons, 227 (51.0%) overtime games were won by the home team, 201 (45.2%) were won by the visiting team, and 17 (3.8%) ended as a tie. Counting ties as a half-win, that gives the home team a 52.7% win rate,

Note that since 1974, the home team has a 57.8% winning percentage in the regular season and a 66.0% winning percentage in the playoffs.

That 12-4 run for home teams in the playoffs

As noted at the above link, the last 16 playoff overtime games have gone 3-1 for the home team. I'd like to be able to say something about statistical significance here, but my one statistics class was a long time ago (and poorly understood even when it was more recent).

What I can do is run some empirical expermiments, under the following conditions:

  • Assign a home win a probability of 55.6%.

  • Simulate 27 games by generating a random number, and choosing a winner (Home or Visitor) based on that probability.

  • Run this simulation repeatedly, and count how many times the 27 games end with 12 (or more) wins for the home team.

Based on the above simulation (and assumption of probabilty for a home win), it lookes like the probability of a 12-4 run is about 9.2%. Which means it's unusual, but not ridiculously unlikely.

Certainly, this agrees with my intuiton, that 27 games (particularly over the course of 52 years) is pretty thin data to draw any strong conclusions from.

Future analysis

I've actually been avoiding the main complaint against the current overtime system—that the team that wins the toss often scores on their first drive.

I have (mostly complete) play-by-play listings for all regular season (and playoff) games going back to the 2001 season, so at some point I will take a look at the 145 regular season overtime games in this period and see how often the "win the toss and immediately score" scenario happens. (Analysis for the playoff games during this period is here.)


It's clear that (even without the numbers on "win the toss and score immediately") losing the coin toss doesn't automatically mean lose the game.

I'm not particularly sympathetic to arguments that the Vikings were somehow cheated in the NFC Championship Game because they never got the ball on offense in overtime. The fact is, if they had managed to hold on to the ball in regulation, they likely would've won easily. And starting on defense in overtime is a disadvantage? Tell that to the Cardinals.

Still, I'm not totally adverse to some kind of "first to score six" modification of the overtime rules. I just think the "unfairness" of the current system has been overstated.