THE BOOK--Playing The Percentages In Baseball

Monday, November 02, 2009

WPA for NFL defenses

Brian Burke gives it to us.  I don’t understand his comment here:

For example, the 2000 Ravens defense had a -6.0 WPA and would have won 12 games had their offense and special teams simply held serve, making absolutely no contribution toward winning. Why 12? Every team starts with a 0.50 probability of winning each game, and it only needs to net +0.50 to win.

I don’t know what he means by “making absolutely no contribution toward winning”.  Does he mean a WPA of 0 (meaning being average)?  Does he mean being replacement level?  In any case, it looks to me what he did was take 6.0 divided by 0.50 to get to 12.  This is incorrect.

6.0 means that the Ravens would win 14 games, if the rest of the team (offense, special teams) was average.  For them to win 12 games, that would mean the rest of the team would be 2 wins worse than average.

Anyway, I love the work.