Do injuries affect performance?
It's my considered opinion that we generally don't give enough weight to the impact of injuries. If a player's on the DL, we know he's hurt (well, usually). But if a player's not doing as well as we think he should, we think he just stinks. Or that maybe he's not trying hard enough.
But I believe that when a good player is playing as poorly as Quentin is playing, often it's because he's simply not healthy enough to play as well as he should. Quentin will be 25 next month, and his professional résumé entering this season was impeccable.