From the videos I've seen about this incident, it looks like an argument which led to a misunderstanding that got escalated. Both are at fault, but I put more blame on the cop.
If the officer actually called a girl a ++++, even if she was on his property it was completely unnecessary and could've prevented everything. Whether the kid said he was going to shoot or sue him, he shouldn't have held on to him the entire time. The kids shouldn't have started attacking him and pushed him over the hedge. If you look at the kid who jumped over the hedge you can see he starts to reach for something in his back pocket. The officer clearly thought he was reaching for a weapon, whether he was or not we'll probably never know.
Then the gun comes out, he's clearly holding it with his non dominant hand considering how awkward he looks holding it. I don't know if he was just pulling it out to get them to stop or to fire a warning shot. But he definitely didn't mean to fire it at that time and he should be glad it didn't hit the kid or someone else, that'd be a whole new mess.
The cop should've handled that situation in a better way.