Let's be honest for a moment. If you take away the 38 points we gave up to New England, this Bengals defense isn't playing poorly despite adversity and injury. The Bengals defense has allowed 10, 17, 20 and 14 point along with the 38. That doesn't look like a defense prone to be scored on - that's after all, the point. The defense has a -4.1% DVOA* (Defense-adjusted Value Over Average) and the 6th best pass defense (-19.5%). This means the Bengals are playing above league average with all things being calculated as equal.
Against the opposing #1 wide receiver, the defense is third in the league with a -28.3% DVOA. Against the #2 receiver, the defense has a -0.3% adjusted value. The Achilles heal is that running backs have a 12.7% DVOA. That means the opposing running backs have a good deal of success out of the backfield. Twelve different backs have caught at least one pass totaling 29 receptions for 262 yards. A majority are 5-8 yards from the line of scrimmage finding holes where the linebackers were or should be.
Compared to last season, the Bengals defense is better. This season's -4.1% is better than last season's 1.0%. The pass defense last season was ranked 13th with a -0.7% compared to this season's -19.5%.
The only difference this season is the stinking rush defense. Last season the rush defense was 24th with a 2.9%. This season it's 12.1% (27th).
The rush defense, as a monkey puffing on a cigar in the middle of a men's country club will acknowledge, is bad. They are ranked 27th with a 12.1% -- meaning opposing offenses have a 12.1% success rate per play. Again, this is computed to make all things equal (explained here)
* DVOA breaks down every single play of the NFL season to see how much success offensive players achieved in each specific situation compared to the league average in that situation, adjusted for the strength of the opponent.
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