To everyone saying that the guy was already disruptive when the cop showed up and the passenger shouldn't have grabbed him-
A) If the guy was that big of a threat officer windmill should have turned his fucking back to him
B) In numerous other cultures it is incredibly common to make physical contact with someone, especially when you're trying to make a point or feel someone isn't understanding.
There's no way the cop should have reacted like that period. Either the dude was a threat that should have been detained before any of that happened, or the cop should have calmly turned around and deescalated the situation. Mother fucker wildly decked a guy over the top of a toddler with clearly no plan beyond that. He's lucky the mob he created didn't't put him in a coma.