That was just pathetic on the part of the Bengals fans...throwing shit at an injured player being carted off the field, and then cheering the injury. The hit wasn't bad, imo, but really.
Leading with your helmet is illegal when the person you are pursuing is not an active runner, this applies in the nfl and college. If you didn't put your head down as a defender when, say, Jeremy Hill is coming at you, you're gonna get trucked...The hit on Ben wasn't great, but it was no cheap shot.