QUOTE (Thirteen Below @ Sep 24 2009, 07:41 AM)

my question is - if this offensive line is basically the same line as last year's, what the heck happened?
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Were they a mediocre line with key vulnerabilities that have just now become exposed? Is it bad coaching? Is it pad level?

The make-up of the line is very different from last year's. Sunday in St Louis, there will only be one starter lining up in the same position as last year: Scott Wells at center. (You know, the guy who lost his job in the offseason.) For the rest, Sitton has four starts at RG, Barbre has two at RT, Spitz has I think five at LG, and Colledge just one at LT. That's a dozen in total.
The most important factor in line performance is stability. Lines play as a unit. It's difficult to do that when the guy who usually plays outside you now plays inside you.
The Packers had returned the same personnel on the line for three years until the end of 2008. In the offseason, McCarthy decided to blow up the unit. Weaknesses in the running game led him to believe the line needed more power up front: hence the new right-half of the line (and demotion for Wells). The previous starters, Tauscher and Spitz, were good against the pass last year, rotten in the running game.
But the left half needed attention too, especially in pass protection. Clifton gave up more sacks last year than in any season since 2001. Colledge gave up more sacks than any other left guard in the nation apart from Alan Faneca. Rodgers, who has been criticized for holding onto the ball too long, made the line look better than it was by rolling out of the pocket more often than any other starting quarterback in the league. He was also very effective throwing on the run (and scrambling).
This year, Rodgers is staying in the pocket more. (A good idea in the long run, for health and safety reasons.) Half of the sacks he has taken came when Colledge and Barbre whiffed one-to-one on a pass rusher — McCarthy absolutely has to adjust the protection more quickly when one of his linemen is getting beat. There were communication problems in identifying blitzes when Spitz was playing center. And the running game is sadly reminiscent of last year's: slow-developing stretches and holes not being where they should be for Grant to cut through.
So, in answer to your question: inexperienced personnel; individual errors; schematic mismatches; insipid play-calling; lack of adjustment; and opponents who boast good pass rushers and effective schemes.