Not sure why He is in that Hospital. A major Head Trauma unit for the VA is only about 30 miles from there. Prehaps He cannot be moved, or maybe not a Veteran.
If appears the police were firing tear gas grenades into an area sparsely occupied by a group of protestors. I think he was just unlucky enough to be in the way of a projectile arcing in. As far as the flash bang allegations go, none of the film I've seen show any flash bangs. I see a some gas grenades popping off.