I was at the game and I'll admit, in the heat of the moment, I cheered.
My Dad and I were standing, cheering the play when I realized he was down. I tapped my Dad and yelled "Cassel is down!, Cassel is down!". I continued clapping, then yelled "C'mon Brady, show us how to play quarterback!... C'mon Brady!"... Dad doing the "Woohoo!" thing... I looked around and noticed almost everyone around us sitting down, with several people staring at us. That's when I realized, oops, that might have been a bit insensitive. Feeling guilty, I sat down and cheered when he got up.
I guess my point is that while there were a few cheers for him going down, I think a majority of the people took the more "classy" approach.