FanPost

Red zone defense and regression to the mean


So remembering my stats class, I decided to take a look at what kind of defense we might expect next year based on what happened this year, adjusted for a little regression.  In a nutshell, regression states that some things which are far outside the norm are not predictive that this future thing will also be outside the norm, and will instead regress to the average. 

This applies to the Eagles in Red Zone Defense.  As we all know the 2010 Eagles RZD was historically bad, giving up a TD an almost unbelievable 78% of the time, compared to the league average of just 53%.  Is this a trend, or an outlier?  Let's look to see what Football Outsiders (FO Almanac) has to say:

Although play in the red zone has a disproportionately high importance to the outcome of games relative to plays on the rest of the field, NFL teams do not exhibit a level of performance in the red zone that is consistently better or worse than their performance elsewhere, year after year. The simplest explanation why is a small(er) sample size and the inherent variance of football, with contributing factors like injuries and changes in personnel.

If we look at 2009, the worst teams in terms of RZD were the Giants at 68%, this year they were 53%, the Bears (66% in 2009 to 47% in 2010), Houston (65% in 2009 and 68% in 2010, they suck), and Green Bay (62% in 2009 to 47% in 2010).  So there seems to be a general trend that 3 of the 4 teams who were worst in the league in 2009 were above average to excellent in 2010.  I don't think it's a coincidence that the 3 teams who improved all were in the playoff hunt, with 2 of them making it and are still alive in the NFC.

Well, could it be McD?  In 2009, the Eagles, his Eagles, had a RZD of 56%, so it's not like this is a known flaw in him.  The odds are pretty great that the Eagles will have a defense at least league average in RZD next year.  To get an idea what impact this may have next year, I took another look at 2010.

If we were to assume the Eagles played 2010 over with everything the same only with a league average RZD, our scoring defense would improve a whopping 2.8 points per game, which would move us from 21st to 14th in the league in scoring D (we're 12th in yards, so this makes sense).  I we were to imitate Green Bay and improve our RZD to 47%, our scoring D would improve 3.4 points per game, which would propel us to 11th in the league.

There will certainly be a lot of change between this and next year, but if you buy into the idea that the 2010 RZD does not mean anything in terms of predicting 2011 performance, there's every reason to expect that our scoring D will be sound next year, even near top 10 material.  All past signs indicate this is so, and I fully expect that the RZD will not be a problem next year, and that our overall team D will improve, as will our record.

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