I brought up Manny Diaz’ philosophy last week and a couple of bloggers of a more statistical bent than I explored the topic as well.
At Football Study Hall, Chad Peltier did a little regression analysis on the subject and found that Diaz wasn’t full of shit.
There’s enough evidence to reject the null hypothesis that there isn’t a relationship between defensive rushing S&P+ and turnovers gained. Rush defense doesn’t explain the whole variation in the data on turnovers gained (r squared is .14), but the two variables do seem to be related in a non-random way (at the 95% confidence level).
In short, the stats do seem to support Diaz’s argument that a defense should work on stopping the run first and foremost for more turnovers.
And today at Team Speed Kills, David Wunderlich does a little statistical exploration, finds some correlation, but wonders if there’s more to it than what Diaz suggests.
But wait a second. Let’s apply a different truism, this one from Football Outsiders: “You run when you win, not win when you run.” As Aaron Schatz explained it:
There are exceptions, usually when the opponent is strong in every area except run defense… [h]owever, in general, winning teams have a lot of carries because their running backs are running out the clock at the end of wins, not because they are running wild early in games.
Apply this to a defensive context, and winning teams will defend more passes than runs. Certainly it’s possible to have a great defense that doesn’t win a lot of games—see Auburn and Tennessee in 2008, or Florida in 2013—and it’s possible to win a lot of games with a terrible defense—see 2011 Baylor, which won 10 games despite being 113th in scoring defense. There are always exceptions, and that’s why these correlations are in the +/- 0.300 to 0.400 range rather than, say, the +/- 0.700 to 0.800 range.
Still, teams that win a lot of games usually have good defenses. We should also expect that good defenses will force a lot of turnovers. We’re now stuck in the correlation vs. causation trap. Does strength at stopping the run cause a team to generate more turnovers? Or does simply being a good defense cause that unit to both stop the run and generate more turnovers?
I’ve always believed that context matters, so I would be stupid to dismiss David’s qualifiers there. But it’s worth mentioning that Louisiana Tech, while leading the nation in turnovers last season, finished 9-5. Take that for what it’s worth.
In the meantime, let’s see what Diaz does in his second tour of duty at Mississippi State. As David concludes,
One thing I can say for sure is this: when you share a division with Nick Saban, Bret Bielema, Gus Malzahn, and Les Miles, focusing on stopping the run isn’t a bad plan.