I can see why this looks excessive, but I don't really think the guy was trying to do anything wrong-they were all over him, and both girls had their hands near his belt (and therefore, his gun, amongst other things on the belt).
That's a completely idiotic thing to do, not to mention how dumb it is to get that hostile just for what was initially just questioning, not even an arrest.
If they had acted normally, they probably would have just gotten a warning from the guy, but they went nuts and tried to hit him, so he reacted that way. I can't say I blame him, honestly, because people in public are crazy and his first instinct isn't about the crazy person's rights, but his own safety and that of the people around him. Not saying he was completely justified- he probably could have done something else defensive instead of hitting her- but I definitely don't feel bad for those girls at all.