That Much-Maligned Eagles Secondary

Look, I understand the Eagles' secondary hasn't been completely up to snuff this year.  Opposing quarterbacks are completing over 65 percent of their passes and there seem to be way too many plays when a ball goes out to a receiver and we don't have a coverage guy anywhere on the TV screen (to be fair, I don't have HDTV).

And what's sort of strange is that the rest of the defense has been playing very well.  The run defense has been solid and the defensive line was all over Carr, Manning and Smith.  The Iggles are tied for the league lead in sacks, with Baltimore, at 16.  Opposing quarterbacks aren't exactly digging in back there.

So the secondary has replaced our linebacking corps as the fashionable new thing to worry about for a fan base that is alwaysalwaysalways looking for the one weak link that's going to come back and bite us in January.

(Can you really blame us?)

Here's the thing.  First of all, it's hard to judge how good these guys really are when they're playing without Lito Sheppard and Rod Hood, our #2 and #3 cornerbacks (Brown is better than both).  And even though the numbers aren't great and there have been some memorable slip-ups, one thing no one has yet pointed out is how much improvement has been made in one crucial area: long completions.

Since the 2000 season, the Eagles have had a pretty good pass defense, finishing most years ranked pretty high in terms of sacks, yards-per-attempt and completion percentage.  Take a look at the following chart.  It's the yards-per-attempt and yards-per-completion numbers for Eagles' opponents since 2000:

Two things stick out.  First of all, the yards-per-attempt number has slowly been going up for a few years.  It's even higher this year, but that's mostly a function of opposing quarterbacks completing such a high percentage of their passes against us.  That will even out.  (The mighty Chicago defense is at 65.9 percent, so don't worry too much yet.)

The key number here is yards-per-completion (the blue column).  For years it held pretty steady at just over 9.5 yards.  Last year it blew up to 11.2 yards per completion, reflecting the fact that opponents completed a lot of big passes against us.  This year it's back down to 9.97 despite the fact that we've been playing without Sheppard and Hood.  That's BIG.  That puts us in a virtual tie for 11th best in the league (interestingly enough, Baltimore again) and suggests that maybe these guys are going to be OK once they all get back healthy.

These numbers got me thinking, so after I put that part together I stared at them a little longer, to see if they revealed anything else interesting.  Just for kicks, I ended up running a couple of quick and dirty correlation analyses with the passing statistics for the entire league in 2005 just to see what came up.

I found something kind of interesting.  In 2005, the correlation between sacks and opponents' passer rating was surprisingly low.  Leaguewide, the correlation coefficient was just -.060.  That's miniscule.  I was actually pretty surprised to see that, given all the stories we hear about how important a good pass rush is.  I thought lack of time would lead to more bad decisions and lower passer ratings, but that doesn't seem to be the case. 

The numbers are very different, however, for a couple other categories.  The correlation between sacks and yards-per-attempt was -.205.  And for sacks and yards-per-completion it was -.414.

Now THAT is interesting.  It tells us -- again, in a back of the envelope kind of way -- that sacks have a much more significant impact on the average length of completions than they do on other aspects of the passing game. 

This suggests that there's a feedback mechanism here.  Teams that are having trouble slowing the pass rush are likely changing to a quicker passing scheme, with more three-step drops that don't require the linemen to hold their blocks as long.  The result is that passes keep being completed, but for shorter distances.  On the flip side, teams that can't pass rush are going to be giving up a lot of big plays, which is exactly the position the Eagles were in last year.

I'm betting on continual improvement for the unit this year, as the Eagles DBs get used to playing with a great pass rush and start tightening up their coverage a bit by understanding that the defensive line isn't going to let them get beaten deep too many times.  I'll check in on these same numbers in a couple of weeks to see if that is indeed the trend.  In the meantime, don't worry so much, these guys aren't as bad as you think.