September 30, 2016

Watching Trees Decompose

By Bill Barnwell, Football Outsiders – special to BSMW Patriots Game Day

Watching Trees Decompose

Last week’s injury to Rodney Harrison was the latest in a seemingly-interminable series of injuries that has decimated the Patriots secondary for the better part of three years. The reason why this injury bug has bitten the Patriots secondary repeatedly isn’t in the numbers: educated guesses, though, would seem to indicate one or more of the following things are the case:

  • Several members of the Patriots secondary are old and/or injury-prone.
  • The Patriots face so many passes by virtue of being ahead in games so frequently that their defensive backs are more likely to get hurt.
  • There is something about the way the Patriots secondary trains and/or is used in games that makes them more injury-prone than normal.
  • The Patriots have happened to hit three years of bad luck when it comes to the health of their defensive secondary.

I will admit that, personally, I am inclined to think that the third choice above is the primary answer, with choices one and four having some relevance as well. Unfortunately, it’s difficult to ascertain what the root causes of the Patriot training or defensive back usage are that would lead to such injuries without doing seriously intense microanalysis, including analyzing how the Patriots train, something I obviously cannot do. At some point, though, Bill Belichick has to give some serious thought into analyzing what he can do to ensure that his defensive backs stay healthy — whether more liberal substitution, a change in how they build up their health for the season, a different offseason program, something! Because, as I’m about to show you, the Patriots defensive secondary is the most injury-hit in all of football by a substantial margin.

At Football Outsiders, we’ve compiled a database containing all player injuries from 2002-2005. Now, it’s very important that I make two notes — first, while the database should be complete, it is entirely possible that a minor injury here or there could be missing. That’s mainly because, second, the injury database is based upon the weekly injury reports issued by the NFL. Of course, Bill Belichick is famed for, let’s be honest, blatantly manipulating the injury report. He’s not the only one, but he may be the most prominent. To correct for this, we’ve also noted what players listed on the injury report actually did that week — whether they started, substituted, or didn’t play at all.

As a measure of whether Bill Belichick is any more of a liar than the average NFL coach, let’s take a look at the what he’s most famed for — listing guys as questionable whether they’re going to be playing or not. From 2002-2005, Belichick has named 78 defensive backs as questionable in his injury reports, the most in the NFL. On the other hand, there have been 1099 defensive backs in the NFL over that time frame that have been listed as questionable. Below, you can see the percentage of those players listed as Questionable who started, came off the bench, or didn’t play at all:

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As you can see, the differences aren’t that dramatic — a slightly higher percentage of Patriots defensive backs listed as questionable ended up not playing, with slightly fewer starting altogether. With that in mind, I think it’s reasonably safe to assume that Belichick’s manipulation of the injury report is slightly overstated, at least for defensive backs.

So now, let’s see if the numbers match up with perception. I noted how many times a defensive back appeared on each team’s injury report from 2002-2005, including players listed on injured reserve. I separated the players into those listed as Probable, Questionable, Doubtful, and Out/IR. Furthermore, since a player listed as Out or on Injured Reserve is much more likely to be injured (remember Troy Vincent, now) than one merely Probable, I calculated a simple weighted score for defensive back injuries, with a “Probable” injury worth 1 point, “Questionable” worth 2 points, “Doubtful” 3, and “Out” or “Injured Reserve” worth 4.

The results? Patriots defensive backs have been significantly more injured over the last four seasons than any team in football.

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As you can see, the Colts, surprisingly enough, had the most injuries to their defensive backs over the four-year span, but that was due to a dramatically high number of players listed as Probable. If you look at the weighted score, no one comes particularly close to the Patriots.

The remarkable thing is that nearly all of the figure comes from the last two years — the Patriots were only 19th in weighted injuries in 2002, and 24th in 2003 (when they listed DBs as questionable 18 times but not a single one as Probable, Doubtful, or Out); they were 3rd in 2004, and in 2005, they were remarkably…sore.

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The Patriots are the only team to have two appearances in the top five — the 2002 Bengals are 10th. Furthermore, the second-place ’05 Broncos are closer to seventh than they are to first in weighted injury points.

I wondered about the second possibility I listed at the top of the article; do the Patriots suffer more injuries because they’re ahead in games and, therefore, have their defensive backs doing more work than other teams — or, alternately, have more defensive backs on the field than other teams because they’re in more passing situations?

The answer is no. The correlation between passes attempted against a defense and a team’s weighted injury score for their defensive backs is .002. Between passes attempted against and sheer number of injuries, that correlation rises all the way… to .01. The two items have nothing in common.

So then, there’s evidence that over the last four years, the Patriots defensive backs have been the most injury-riddled in football. How about 2006, you ask? Well, we don’t have all the injuries compiled as of yet to compare the Patriots against, but going through the injury reports for this season, they’ve already compiled 76 weighted points through the first nine games (including this week’s report) of the season. That leaves them on pace to record 135 points for the season, which would’ve been in the top 5 for weighted DB injury points last season; furthermore, with Randall Gay on IR and Rodney Harrison out indefinitely, that number is likely to rise. Forget an injury bug; the Patriots secondary, at this point, is begging for an exterminator.

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