They're not trying to injure him, they're taking advantage of a perceived weakness. That's not bush league: as the legendary Herm Edwards once told us, "You play to win the game." If there was a catcher who had the yips throwing back to the pitcher, taking second on such a throw would also be perfectly acceptable.
CC has shut the Sox down all year, so trying new strategies to get runner on against him would be smart even if he wasn't battling a bum knee.
Had the Yankees bunted all over Schilling during the bloody sock game, that would have been perfectly acceptable (hell, it would have been very smart).
Baseball players are, in general, enormous babies. CC is merely following the trend here.