In 2010, the Packers had the fifth-best defense in the league in terms of total yardage (309.1/game). In 2011, they had the worst defense in the NFL, surrendering 411.6 yards per game. They went from allowing 15 points per game (second in 2010) to 22.4 per game (16th), they allowed 2011 opponents to convert 43% of their third downs, 26th in the NFL (up from 36% in 2010, ninth-best in football) and allowed 29 passing touchdowns, up from 16 in 2010.
No point in discussing rushing defense, sacks, etc; you've heard it all before. All told, it was one of the worst year-to-year defensive collapses in Packer history.
Why this happened is still a matter of much debate. The popular "domino theory" has to do with the loss of two key players from 2010: Cullen Jenkins (free agency) and Nick Collins (neck injury in Week 2). Jenkins' departure left the defense with only one proven pass-rusher, outside linebacker Clay Matthews III. The situation got worse when Jenkins' replacements flopped and no other pass-rushers emerged. Opponents were able to focus on Matthews and minimize his impact, and with no consistent pass-rush, opponents had more time to pick the secondary apart. Collins is one of the best safeties in the NFL when healthy, gifted with great speed and range; his loss further hamstrung the defense and led to the secondary's terrible year.
Another theory is that the Packers were simply on the wrong end of history. 2011 was widely hailed as the Year of the Quarterback, and Green Bay faced some of the NFL's premier signal-callers in 2011. Drew Brees, Matthew Stafford, Eli Manning, Phillip Rivers and their ilk didn't just pick the Packers apart, they picked everyone apart. Surely, the logic goes, one cannot blame Green Bay too much for getting skewered; they play in a quarterback-heavy conference and faced some of its best in 2011. (Bolstering the argument is the fact that eight of the top 10 pass defenses last year were AFC teams, far from Brees, Stafford, Manning, Cam Newton and Aaron Rodgers).
Both of these theories have their merits, and both deserve to be part of the final explanation. However, they're also incomplete and full of excuses. Thirty-one other defenses faced elite quarterbacks in 2011 and weren't as terrible as Green Bay was, and the domino theory leaves a lot unexplained. Why did established starters such as Tramon Williams, A.J. Hawk or B.J. Raji take such huge steps backward from their 2010 levels of play? Why did backups such as Charlie Peprah, Sam Shields, Erik Walden or Howard Green regress as well?*
Apart from a few players, such as Matthews, defenders often appeared to give minimal effort and lacked fundamental football skills, such as tackling. In one of the season's defensive low points, Tampa Bay running back LeGarrette Blount broke tackle attempts by Desmond Bishop, Morgan Burnett, Williams, Hawk, Shields, Ryan Pickett and Walden, and avoided the halfhearted attempts of Peprah and Charles Woodson. If you watch the play, available on YouTube, there is a complete lack of heart or desire from the Packers' defenders on that play. Nobody wants to wrap Blount up and bring him to the ground. It's a pathetic attempt at NFL-caliber defense, and while it wasn't this bad all season, the Packers certainly didn't improve much from this point in the final two months of the season.
The domino theory just doesn't account for the way that all those players took a step back, or why the Packers lacked effort and energy and heart all season. So who's to blame? A certain amount must go to the front office, which was relying on Mike Neal to fill Jenkins' role. General manager Ted Thompson also re-signed Peprah to be the third safety, a move that backfired when Collins went down, and chose to rely on Walden and Frank Zombo at right outside linebacker.
But if you're looking for a systemic explanation of why the Packers failed so epically on defense last season, I would point to a combination of the Super Bowl victory and the way Mike McCarthy runs the team (at least the way we see it as outside observers).
The phenomenon of a Super Bowl hangover affects every SB-winning organization. It's hard to get your players back to giving the phenomenal effort that NFL players have to give, every day in practice and every Sunday on the field, when you just won the most coveted prize in football and everyone from the media to the fans are hailing you as geniuses and saviors. Some coaches manage the transition to the next year better than others, while some are simply better equipped to speak to the whole team than others.
You see, McCarthy is an offensive head coach and always has been. Throughout his tenure, McCarthy has been heavily involved in the offense and has largely left the running of the defense to his defensive coordinators, Bob Sanders (2006-08) and Dom Capers (2009-present). Whether that's right or wrong, from an outsider's perspective, it certainly looks and feels that way. From an organizational standpoint entering the 2011 season, McCarthy was well-positioned to coach the offense through any potential Super Bowl hangover, and it worked; the offense had a phenomenal year, young players such as Bryan Bulaga, T.J. Lang and Jordy Nelson made massive improvements, and Aaron Rodgers won the MVP for being awesome.
However, the defense wasn't in a position to get the lion's share of McCarthy's attention, and had to make do with Capers and his staff instead. Based on the result of the season, it appears that Capers wasn't able to coach them through the Super Bowl hangover the same way McCarthy managed his side of the ball. While half the team excelled in 2011, the other half fell flat. I think that's a direct result of McCarthy's being an offensive head coach, and the fact that Capers and his staff are great at drawing up defenses and scheming--that's Capers' main strength--but perhaps not so good at motivation and instilling any kind of espirit de corps. Young defenders like Raji or Shields didn't have external motivation from Capers or internal hunger to go win, and as a result, they turned in half-arsed performances all year long.
This theory can't really be proven unless you're inside the Packers organization, which I'm not, and have the opportunity to observe them from inside, which I don't. I certainly don't think that an untreated SB hangover was the only problem in 2011; lack of talent on the defensive line, at safety and at ROLB and facing some of the league's best offenses didn't help anything.
But the recent Super Bowl victory contributed to a lack of motivation that Capers and his staff were unable, apparently, to fix. I think this issue has a chance to fix itself in 2012, one year removed from the Super Bowl win, as well as McCarthy hopefully spending more time with the defense. It's time for the Packers' defensive talent to play up to its capabilities again, and I think there's a chance that could happen in 2012 with the proper assistance from McCarthy.
*I give Morgan Burnett a pass because he was playing his first real NFL year last year; remember, it took Collins three years to put it together. Bishop, Woodson, Matthews and Pickett all had decent-to-good years, although Bishop and Woodson probably regressed slightly from their 2010 form.