People's fault. The cop claimed he was hit by a snowball, and with as reckless as the people were acting, I wouldn't doubt it that someone said "Hey, throw a snowball at that cop's car".
He might have overreacted by drawing his gun, but if that snowball hit his windshield, that could've caused an accident and now you're endangering his life. I'm sure he didn't wake up and say, "Hey I think I'm gonna ruin a whole bunch of people's fun today." No, you put his life at risk, and he felt the need to do what he did.
The second officer who was talking to the people was calm, polite, and did everything he could to help the situation. The people were idiots. You don't like the police? Then, the next time when someone breaks into your house in the middle of the night, and you're hiding in your closet, don't call 911.