We might be halfway through the first quarter of the first NFL playoff game of 2013, but I’m still finishing up with baseball and just getting warmed up on football. Football month on the blog officially kicks off today — there’s lots of interest stuff to come, from innovative rule ideas and play calling to new prediction methods and game analysis. Today, I’m trying an addition to the measure of NFL team quality that I debuted last year: True Wins. True Wins are calculated as follows:
True Win = Blowout Wins + Close Wins/2 + Close Losses/2 + Ties/2
You may recognize the intuition from pythagorean expectations — you get full credit for blowout wins (I define this as more than 7 points), but no extra credit for winning by huge margins, and you get half credit for all close games, since those probably come down to luck more than skill. Last year, I showed that True Wins predicts a little better than pythagoreans, and it’s a whole lot more direct. Both measures are much better than using wins alone, which unfairly penalize (reward) teams that lose (win) a lot of close games.
What Else is Luck-Driven? Fumble Recoveries?
With the playoffs coming right up, I decided to try an improvement that adjusts for possible luck in fumble recoveries as well. Here’s the logic (from Football Outsiders):
Stripping the ball is a skill. Holding onto the ball is a skill. Pouncing on the ball as it is bouncing all over the place is not a skill. There is no correlation whatsoever between the percentage of fumbles recovered by a team in one year and the percentage they recover in the next year. The odds of recovery are based solely on the type of play involved, not the teams or any of their players . . . Fumble recovery is a major reason why the general public overestimates or underestimates certain teams. Fumbles are huge, turning-point plays that dramatically impact wins and losses in the past, while fumble recovery percentage says absolutely nothing about a team’s chances of winning games in the future. With this in mind, Football Outsiders stats treat all fumbles as equal, penalizing them based on the likelihood of each type of fumble (run, pass, sack, etc.) being recovered by the defense.
The keys are:
- Fumbles are huge turning points in games
- Teams don’t maintain high or low recovery rates over time
To quantify #1, I determined the point value of a recovery. A simple regression of point differential in each game on total fumbles and fumbles Continue reading