As weird as this may seem, they would probably assume it was a fight. In 2011, I roomed with this girl in Chicago and her best friend Gary lived on the first floor of the apartment building that we lived in. About 2 AM one night (I had only been living there a month at the time), Gary was pounding on the door and he was COMPLETELY drenched in his own blood. His boyfriend had been beating the crap out of him. I had to sit with him in the bathroom while he cried and bawled and kept apologizing to me that he was bleeding. It just made my blood boil that he could have been degraded so poorly by his boyfriend to think that getting beat up could be his fault in any way. well, the boyfriend came pounding on the door while I was sitting in the bathroom and I opened the door and knocked the motherfucker onto the floor.
Although I technically wasn't arrested for it, since the perspective was that the boyfriend was there to beat Gary up even more and I was defending him, I did have to go to the station to talk to the police for a couple hours.
I also once had to hit a guy in a parking lot who was stalking his ex wife, who was a friend of mine, and was threatening her and not letting her get to her apartment. So the only times I have ever had dealings with the police are because of those reasons, so they'd probably assume it was a fight. Which honestly makes me sad because even though I've hit two people and I spar with karate partners all the time, I really, really, really, really hate violence.... it's probably why I like wrestling so much because it's simulated violence. I do NOT want to be known as a guy who gets into fights
Lord, why can't I just answer a question without giving a life story....