From what I've been reading in these comments, I think people are only looking at it as "self-defense." There are multiple things going on here. To start off, he is breaking up a fight, with what looked like a guy on the ground. There is legal justification to go in and stop that--defense of others. We have laws protecting us when we try to help out in events like this, but nobody is ever really told about them.
Later on, the same people target him, then. By that point it is self-defense. After all, the one guy charged at him and, after being sprayed, swung at him as Phoenix backed away. They were even calling the cops as it was going on.
I'm not saying it's right to go around beating people up, but he didn't do that here. He had justification to do so. Also, the cops took a while to get there, even though there were fights breaking out and a hit-and-run. Who knows what would have happened if it wasn't interrupted...