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Rush defense and generating turnovers, part two

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What happens if we isolate the effect of rush defense from pass defense on generating turnovers?

Brad Barr-USA TODAY Sports

Last week I ran a regression between defensive rushing S&P+ and total turnovers gained data from last season to test Manny Diaz’s argument about the importance of run defense for turnover creation, but there were two things that could have been better.

First, I could have tested the data for not just total turnovers gained, but specifically interceptions, which is even more in line with Diaz’s theory. Second, I could have controlled for Def. Passing S&P+, which would test not only whether run defense is related to turnovers, but whether having a good run defense is more important than having a good pass defense for generating turnovers.

So that’s what I did.

The results were interesting, especially if you’re a Mississippi State fan. I ran two regressions that both included Rushing S&P+ and Passing S&P+ as independent variables on total turnovers gained and interceptions per game. In both cases, Rushing S&P+ was statistically significant and positively related to the dependent variables – and Passing S&P+ wasn’t.

I want to be careful with how much we generalize from this data, but it’s clear that these two regressions lend further support to Diaz’s run-stopping theory for increasing turnovers.

I suppose there is still some question about the cause of this relationship. Is the increase in turnovers (and interceptions more specifically) just the result of an inefficient rushing offense simply being forced to pass more often against quality run defenses? You’d definitely expect more interceptions with more pass attempts (unless your quarterback is Marcus Mariota or Cody Kessler, I suppose).

Also, does this say anything about next season? Looking at the best rush defenses from last season, Alabama and Clemson (the top two teams according to rushing S&P+) both had good but not exemplary turnover numbers (averaging 0.79 and 0.92 interceptions per game, respectively). They contrast with TCU, the sixth-best rush defense, which averaged over a full interception more per game last year. Imagine how games might have turned out differently if Alabama’s defense had averaged an extra turnover per game, or for that matter, TCU failed to snag an interception per game – you might have drastically different game results.