Changes in the Bucs defense: pass defense bad, run defense good?

If there's one thing I really don't understand this year it's the decline of the pass defense. The Tampa Bay Buccaneers weren't excellent against the pass last season, but they were decent - certainly above league average. Buoyed by 10 interceptions, the Bucs ranked 13th in the NFL with 23 passing touchdowns allowed and 11th with 5.9 Net Yards per Pass Attempt(NY/A) allowed. NY/A includes sack yardage. 

More tellingly, the Bucs ranked 13th in pass defense DVOA, which takes into account the strength of opponents faced. So this wasn't just a mirage created by the quality of opposition the Bucs faced: the pass defense really was pretty good. 

And then this year, the pass defense has absolutely collapsed. The Bucs have allowed 11 passing touchdowns, ranked 17th in the NFL, but they've also allowed 7.5 NY/A this year, which ranks 29th. Worse yet, they're ranked 29th in pass defense by DVOA. And that's after a decent game against the Bears - they looked worse before last weekend's matchup. 

I have no real explanation for this sudden dropoff. The only change in the back seven was the replacement of Barrett Ruud by Mason Foster. And while that certainly would have an effect, it cannot be this large. Ronde Barber is playing at a slightly lower level than he was last year, but it isn't that noticeable. And while the Bucs have had to play Corey Lynch at safety more than they probably wanted, he started the last games of the 2010 season as well. 

And if you look at the personnel, the Bucs should actually be better in pass defense this year: they actually have a pass rush. Adrian Clayborn has been a really positive surprise, getting better every week and really beating up some left tackles. Michael Bennett has played much better football than he has in previous years. Both Bennett and Clayborn have played much better than last year's starters Kyle Moore, Tim Crowder and Stylez G. White - although Stylez did just win the UFL championship. 

This dropoff in pass defense has been accompanied by a major uptick in run defense, which had been a weak point for the Bucs since the 2008 season. While the run defense is inconsistent, allowing a few too many long runs to really be excellent, they're much improved over last year. The run defense is currently ranked 9th in DVOA, while it was ranked 32nd last season. 

This uptick in run defense is much easier to explain: the defensive line has been very stout against the run, especially so when Gerald McCoy has been in the lineup. In addition, Mason Foster brings a physical presence in the box and has played a big role in improving the run defense. This despite the fact that the safeties haven't played as well against the run as they did last season, with Corey Lynch especially being a weak link. 

I can't explain this sudden change on defense. All I can say is that the Bucs run defense has gotten better, and that's good - but that they need to get the pass defense back on track, quickly.