## How Bad is Rex Grossman?

We keep hearing how Rex Grossman costs the Bears wins. Is that true, and if so, how many wins?

Sure, Grossman's NFL passer rating is the lowest of all starting QBs. He has 1 TD and 6 INTs in 3 games. Clearly that's not good. In this post, I'll estimate how many wins he would cost his team if he were allowed to continue playing at his present level of performance.

The estimate is based on an improved passer rating formula. The components of the new rating are weighted according to how important they are in terms of team wins. The formula is based on a multivariate regression model of team wins. Using data from the past five NFL regular seasons, the regression model estimates team wins based on the efficiency stats of each team including passing, running, turnovers, and penalties. Regression models can hold all other factors equal, so by only adjusting the factors of interest (QB passing, rushing and turnover performance) we can calculate the effect of QB performance on the estimate of season wins.

Further, the rating excludes receiver Yards After Catch (YAC) and relies only on QB Air Yards. It also includes rushing yards, sack yards, interceptions, and fumbles. All factors are computed on a "per attempt" basis. The resulting formula computes the wins added by a QB's performance per a 16-game season, "+WP16" (apologies to David Berri). The equation is:

+WP16 = [(Total Yds/Total Plays * 1.57) - (Total Turnovers/Total Plays *50.5)] - 4.5

Total yards includes air yards, rushing yards, and sack yards. Total plays includes pass attempts, rushes, and sacks. Turnovers include interceptions and half of all fumbles (lost or not). The equation subtracts 4.5 because that is the average +WP16 score for QBs in 2007 so far. An average QB on an average team would win 8 games, not 12.5.

So for Rex Grossman:

+WP16 = [(283 Yds/102 plays * 1.57) - (6.5 TOs/102 plays * 50.5) - 4.5
= -3.4 wins

So holding all other factors equal, Rex Grossman would cost his team 3.4 losses over the course of a full season. Last year Grossman was in the middle of the pack with +0.3 wins added. He did what the Bears asked of him, which was to break even and allow the defense and special teams to make the difference. This year, not so much.

### 2 Responses to “How Bad is Rex Grossman?”

1. Anonymous says:

What happens if you compare Grossman to a Replacement Player, as opposed to the average QB? The Bears are replacing him w/ Brian Griese, not Jake Delhomme or David Garrard (who were middle-of-the-pack last yr in QB+WP16, according to your analysis).

2. Brian Burke says:

Jon- Tonight or tomorrow I'll have the full list of 2007 QB "wins added per 16." The 32nd best QB turns out to be Losman at -3.7, so Grossman would be about +0.3 Wins above replacement.

QB is a high risk-reward position, so I'm not sure 'above replacement' is the best way to think about it. Even though Greise might have replacement level talent, he might mean more wins to the Bears by playing a conservative style that Grossman does not appear capable of.