The folly of pro football

I watch some NFL games but have never understood the attraction of prognosticating. Every year there are a few clearly good teams and a few dogs and about 25 teams in the middle.

And a good season or a bad season, for those 25 middle-of-the-roaders depends largely on luck – specifically turnovers.

Hera are two graphs to explain.

The first shows how important turnovers are to winning. I got it from a Houston Chronicle blog that actually died yesterday. The first post I read was its final post. Weird.


How to win


As you can see, the higher a team’s turnover margin, the more wins it posted. TO margin, turns out, is second-best predictor of victory, after number of rushing attempts. (I discount the latter because teams that lead tend to run to use up time, and teams that trail tend to pass because it kills the clock and it gains yardage faster.)

In fact there’s a tidy formula at the bottom. Every additional turnover you get is worth a bit over one-fifth of a victory. Last year, for example, Green Bay had a +24 turnover margin. That was worth almost five victories for a team that finished 11-5. An average turnover margin could have left the Pack at 6-10.

But how fair is it for me to point to that? Green Bay has an aggressive defense and a careful offense. It will tend to have more takeaways than giveaways.

Enter graph No. 2. This maps turnover margin across years. 2008 turnover margin is on the horizontal axis, and 2009 turnover margin is on the vertical axis. And sure enough, Green Bay, the big yellow dot at the right, has a favorable turnover margin both years. (Margin of +7 in 2008.) What about the rest of the league?


Just wait till this year


If the same teams won the turnover battle year after year, you’d see a strong correlation here and the regression line I’ve plotted would slope upward. Instead, it slopes slightly downward, though it’s so slight I wouldn’t make a big deal of it.

Essentially, I argue that turnovers largely can’t be tamed. A team that does well one year is no more likely to do well the next. And with turnovers so heavily correlated with victory, picking the NFL is about like picking the coin flip.

And here’s the kicker: If you’re in a random situation, you would expect some teams to have two straight years with favorable turnover margins. Green Bay might have been one of those. After five games this year, the Packers have a -2 turnover margin, but they have won three of those games.


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