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Monday, August 13, 2012

Is red zone efficiency really a myth?

Is football outside the 20s different than football between the 20s?

The belief that red zone efficiency is a meaningful statistic centers on this proposition. Aaron Schatz of Football Outsiders argues that red zone efficiency is a myth because it cannot be used to predict future red zone efficiency any better than other offensive statistics--in other words, good offenses move the ball, in the red zone, at midfield, all the same.

But that's for the NFL. A leading argument in favor of red zone efficiency is that certain styles of play are more effective on a smaller field. College football teams are more diverse than NFL teams. (In the technical parlance, we would say that we fail to find a significant relationship with the dependent variable because their is insufficient variance in the independent variable.)

I divide college football teams over the last 5 seasons (a total of about 600 teams) into four categories: Grinders, Paulies, Leachers, and Bikers. Grinders are teams that depend on short yardage run plays: Army has been the poster child of grinding for the last 4 years. Paulies are teams that depend on explosive run plays, named for Georgia Tech's Paul Johnson. Leachers use high percentage, short yardage passes: East Carolina, headed by Mike Leach progeny, is the leading example recently. Finally, the Bikers, named for Bobby Petrino, air it out; Arkansas, Tulsa and Houston have been the most prominent Bikers for the last several years.

The logic of red zone efficiency says that Bikers, especially, would do poorly in red zone situations because the offense depends on stretching the field vertically. Grinders run a goal line offense from one endzone to the other, so they should be unaffected by red zone situations. Leachers and Paulies stretch the field horizontally as much as vertically, and the field is just as wide inside the 20 as at midfield. They should find it harder to move the ball, but should do relatively well compared to Bikers.

And now for statistics. (The analysis is based on 1 million plays since 2007.) All styles struggle in the red zone. Yards per play begin to fall at around the 40 yard line and then plummet inside the 20. There are two leading reasons for this: 1) you can't snap off a 50 yard run when you're 30 yards from the back of the endzone and 2) defenses don't have to worry about you snapping off a 50 yard run when you're 30 yards from the back of the endzone. In the middle of the field, Bikers and Paulies average more yards per play, precisely because they are better at explosive plays.

Yards per play by distance to goal line
Looking closer at the last 40 yards, this next chart compares the performance of the 4 styles relative to the other styles. So, for example, Grinders get about 93% as many yards per play as other teams at the 40 yard line, but 5% more yards when they are inside the 3. Particularly inside the 10, Grinders are better than others and Bikers are worse even when the opposite is true over the other 90 yards.(Technical note: the trend lines for Grinders and Bikers are statistically significant. The relationship between style and yards per play inside the 10 and outside the 10 are also significant.)

Yards per play versus league average
Now that is all fine and dandy, but what really matters is if these teams are scoring points. I started by calculating the average points per possession by field position for each style. I then subtracted the league average from that. So, for example, when inside the 3, Paulies score 1/10 of a point more on average than the typical team. Again, Bikers do poorly inside the 10, especially considering their performance everywhere else. Grinders and Leachers are about league average when they get close to the goal line. My interpretation of this is that Grinders are more likely to make forward progress in the red zone, but less likely to get the play they need to plunge over the goal line than Paulies.

Net net, in college football it does seem that there is a relationship between style of play and red zone efficiency.  And this relationship is the opposite of what we find over the rest of the field. High octane passing offenses especially struggle, with the performance dropping inside the 25 and falling below league average around the 10. Teams with explosive running games--Oregon, Georgia Tech, Nevada, West Virginia under Rich Rod, Michigan, Wisconsin, and Virginia Tech to name a few--offer the best combination of high yards per play across the middle of the field and high points per position in the red zone.

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