I can easily see how this sort of thing happens.
I pulled up to Ralph Wilson stadium for the Bills-Pats game, and a parking attendant directed me into a lot that was like driving through a post-apocalyptic riot scene. It was like Mad Max in there, with trash cans burning left and right in the middle of the road. I was like, why the hell did he send me in here? There were no parking spots anywhere as they had been taken up by tailgaters, and I was in no man's land. Even worse, there were about 4 cars following behind me, and the idea of backing up after driving a quarter of a mile of swerving around people and their fires, well, that wasn't too good. Finally my road was totally blocked by a about 20 guys. Cops came by, and I asked them what to do--and they said, "tough luck." They were having a tough time getting through themselves on their golf carts (actually, I thought one was going to help me, but he just wanted some info about my car--a Subaru WRX, and after we made small talk about cars, he said, sorry can't help you.) I can totally see how a cop's anger level will rise while driving through a tailgate. I'm not defending the cop, mind you, but knowing what a clusterfrig that scene is, you gotta keep your cool and laugh. I had a British friend go with me to the game, and he had never been to a US football game. When we got roadblocked, I got out of the car and walked toward a huge bus. It was the Guy Fieri roadshow bus (the guy from the Food Network). I just walked inside the party bus--wall to wall people, and really the only women around in the whole lot. I left my British friend outside and he later reported to me that he was scared witless because a bunch of Bills fans were chanting ahole at him for blocking the road, and he was probably nervous because he was used to hooligans. Finally, after finding the guy hosting the party, I asked if he could move some tables next to the bus so I could park and he said yes, and even gave me a beer. I parked, had a couple beers, and watched as the people behind me were marooned and practically pulling their hair out as cops kept coming by in golf carts.
In short, the Indy policeman had no reason to attack a fan for obstructing his way. The cops in Buffalo had the attitude: "This is a clusterfrig, and there's not much you can do about it."