Well, cheering for someone leaving the game isn't the same thing as cheering for them being injured
. Cassel had already had a pretty poor performance that game (and all season) with several turnovers and interceptions. As soon as our Seconday got in what did we get? A touchdown. (Eventually taken back due to an Offensive Pass Interference.)
I don't think Winston was as out of line as many have painted him in local media to be as he had some basic points, but I also don't think most of those cheering were cheering for Cassel's injury but simply cheering for the entry of our secondary. More Cheering for Cassel's leaving. Had he been pulled out by Romeo just normally he probably would have gotten cheered too.
Cassel sucks, plain and simple. He's Pioli's golden boy and that's all that's protecting him.