A Synthesis: Sacks And Pass Defense

Earlier I made a post about 2006 SEC pass defense, and also about 2006 SEC sacks, analyzing each separately.

In reality though, considering it is all one defense, the two things are related, or are they? That's basically what I set out to determine. At bottom, is there any correlation between the number of sacks a team generates and how well their pass defense performs? Or does that number of sacks created have little if any correlation to how well a pass defense performs, as Joe Kines contended?

To figure it out, I ran the numbers on how well Adjusted Sacks correlated to a variety of different measures of performance for a pass defense, including opposing quarterback's average passer rating, yards per completion, yards per attempt, completion percentage, interception rate, and touchdown rate.

Before I list the results of what I found, I'll give a very brief primer on correlation for those who may not be familiar with the concept. At bottom, correlation ranges from 1 to -1, and values that that are near 1 or -1 have correlation, and values near 0 essentially have no correlation. Going up to 1 means there is positive correlation, i.e. the more x happens, the more y happens. Going down to -1 means there is negative correlation, i.e. the more x happens, the less y happens.

So, with that in mind, the following is how well Adjusted Sacks correlated to that variety of measures, in descending order:

Opposing QB average passer rating: -.4997
Touchdown rate: -.4693
Completion percentage: -.4660
Yards per attempt: -.4489
Yards per completion: -.3087
Interception rate: -.2573

As you see, opposing team's passing numbers generally tend to go down greatly as the number of Adjusted Sacks increase.

Opposing quarterback average passer rating, touchdown rate, completion percentage, and yards per attempt all have a pretty high negative correlation with the number of Adjusted Sacks. Again, there's just no real way to dispute the data, for the most part. Unless it's just an odd-ball deal with a one year sample size, which I highly doubt given the breadth of the statistics, it generally just showcases that pressuring the quarterback pays off.

I was thinking, perhaps, that would I might find would be a good bit of teams that racked up a lot of Adjusted Sacks did so by blitzing heavily, and that would even things out in the end with that defense giving up a lot of big plays and completions. But, as the breakdown showed, that simply wasn't the case. Certainly some teams did get a high number of Adjusted Sacks by blitzing heavily, but they didn't seemingly give up very many big plays or lot of completions. I suppose it isn't quite like the old Joe Lee Dunn days at MSU, where two sacks would be followed by a 38-yard completion against a seven man rush. You have to give credit to defensive coordinators and other defensive coaches; generally, it seems, even when they bring lots of pressure, the defensive backfield still, relatively speaking, prevents big plays.

The only snafu to the entire analysis was Interception Rate. There was a -.2573 correlation between Adjusted Sacks and Interception Rate, meaning that as Adjusted Sacks went up, the Interception rate tended to go down. Perhaps this should have been too shocking, especially considering the result of LSU, Arkansas, and Alabama, but it still is just a bit. You would think, intuitively, that more pressure would result in more bad throws and more interceptions, but the reverse is true. I suppose that the man-to-man coverage on the outside, combined with the shorter throws when the blitz is expected, means that defensive backs are not in as good of a position to intercept the football. And moreover, again since they are in man-to-man coverage, cornerbacks may not want to be as aggressive, knowing that they would have no help over the top if they made the slightest mistake. I know, it doesn't seem right intuitively, but more sacks correlates with fewer interceptions, at least in this data set. I would point out, however, that a correlation of only .2573 isn't particularly high, so maybe it is just statistical white noise that would work itself with a larger sample size. I suppose we'll see when we run the same numbers this time next year.

At the end of the day, you just have to be brutally honest about it. At bottom, it seems that if you were going to be successful in pass defense, you had to get after the quarterback. If you didn't, you just weren't going to be very good in defending the pass.

As for Kines, I certainly don't want to criticize his philosophy, because obviously he's forgotten more about football than I will ever know, but the numbers just seem to invalidate his defensive philosophy. Kines essentially betted that we could drop seven and eight defenders into heavy zone coverage, and opposing quarterbacks wouldn't be able to beat it. Unfortunately, at least in 2006 (that philosophy worked with all of the talent we had in 2005), that didn't work. Quarterbacks did effectively pick apart the defense with a relatively high degree of regularity, and with that in mind we struggled greatly in terms of pass defense. And, honestly, a lot of that credit goes to opposing quarterbacks. Perhaps there was a time when you could count on opposing quarterbacks to make a lot of mistakes throwing into heavy zone coverage, but that time seems to have passed.

The good news is that with Saban in charge now, Adjusted Sacks will go way up, and that should drive opposing team's passing numbers considerably lower.