the trouble with this is that guy got injured in someway not associated to the flashbang. We see a 15 second clip that shows him already on the ground, but what if it was 4 or 5 gusy who were whipping his ass. When the crowd rushes back in who is to say one of those guys didn't come to finnish the job he started. I have used flashbangs quite a bit, and they are only about a half a pound. A head injury like that doesn't come from a flashbang. Just saying.
the trouble with the video is that it is posted by Occupy. Therfore it is propoganda related to enforce their cause. You do not see what happened for the 5 minutes prior to the crowd being dispearsed.