No one would call the 2010 version a vintage Oklahoma defense.
Was it bad? Not at all. It just wasn't the kind of rock-solid unit that the Sooners are known for.
Coming on the heels of 2009, when Bob Stoops fielded one of his best defenses ever, OU's occasional porousness was surprising.
I don't think anyone in Sooner Nation needs statistical proof that Oklahoma's defense slipped significantly from 2009 to 2010. Just how much may come as a surprise, though.
The Sooners saw their average yards allowed per play (DYPP) climb a full yard, from 4.1 in '09 to 5.1 in '10. That equates to a 23.6 percent increase, third highest in the nation. (Every FBS team's percentage change from 2009 to 2010 in yards per play for both offense and defense, using data from cfbstats.com.)
So, OU's D has to improve this season, right? Not necessarily. It's entirely possible last season was just a case of regression to the mean.
(Note: With the variation in opponents from year to year, we should be wary of making overly definitive conclusions based on cursory data. Instead, consider this more of an outline than a full picture.)
In reality, the 2010 version of Oklahoma's defense actually was close to the program's longer-term statistical profile in a "meta" sense. In fact, the '09 D really looks like an outlier.
OK, I realize that's downer, so here's the silver lining: OU was uncommonly bad against the run last year. When you're allowing more than 4 yards per rush, it can be hard to get teams off the field consistently, especially when opponents are chewing up almost 5 yards every time they run the ball on first down.
The Stoopsian defensive philosophy is predicated on shutting down the ground game on early downs and then firing away at the quarterback on second- and third-and-long situations. When that's not working, the whole scheme can fall apart pretty quickly.
If you want to know why Stoops and his staff are so jacked up about the defense they'll field this season, that probably has something to do with it. The odds that OU will have as much trouble stopping the run in 2011 seem slim.
So, what would be reasonable to expect from the Sooner D in terms of improvement? Well, it stands to reason that teams that go through a significant swing from one season to the next generally swing back towards an equilibrium point. We've also seen that such improvement typically comes at an incremental pace.
In other words, if you're expecting the Sooners to get back to their '09 form, as represented by a 20 percent cut in yards allowed per play, that's asking a lot. Only two teams managed to achieve that degree of improvement last year, Florida State (-26.5 percent) and Florida Atlantic (-20.1 percent).
If winning a national championship this year is contingent upon getting OU's defense back to the '09 level – and I'm not saying that's the case – snagging number eight will have to wait until at least 2012.