Injuries, man. I think 2009 was the last time we've been so decimated by injuries. By my count, we are down about 7-8 opening day starters, including our best and (by far) most important player on offense (Sanders) and now our best player on defense (Lacy).
Mason didn't "inherit" the same defense from last year - not even close. Last year's defense had multi-year starters at every position, including two linebackers who are on NFL rosters now, one of which (Rodriguez) has started every game as a rookie. We had new starters at 6/7 of the back end this year, with Jason Taylor the only returning starter... and (big surprise) he's also been injured.
(This year's defense even with Knowles, and especially considering all of the injuries, would be just as shitty. Knowles is a good DC, but he isn't some wizard, no matter what OSU fans say now. The defense sucked his first few years when he had a largely inexperienced group. Funny how he got really smart as soon as he had multi-year starters at every position.)
In terms of the full team, the last game we played where we were anywhere near healthy was the TCU game in Ft. Worth. Since then, we've been the walking wounded and literally lost more players each game since.
I thought Rangel actually played well given the circumstances and has me optimistic for the QB position post-Sanders.