The game is on TBS, and the announcers haven't said anything about it. On the replays, you couldn't really see him injure anything after throwing the gopher ball pitch, but the trainer and Williams came right out and took him out of the game. He was walking off gingerly which would seem to indicate it was his groin, but impossible to tell for sure. Apparently, however, Williams had already alerted the umpire before that inning that he might have to pull him and Munro was already warmed up.
Oswalt looked way off the whole game. He was constantly getting into jams, and his fastball was topping off in the mid to high 80's so something is definitely wrong with him.