It kind of looks like the dude who beat the nigger here put on some knuckle dusters right before he engaged; he's got some object in his right hand just before he engages, but doesn't have it when he stands up. Not quite sure what it is.

But as to why niggers get knocked out- same reason anybody else gets knocked out, he didn't see the punch coming. In this case, nigger walks right into punching distance after challenging the man to a fight with his hands down at his fucking waist, like he's some hot shit thug. Then a left shovel-hook comes up fast and smashes his jaw before he even sees it coming- you can see how slow his reflexes are, because both of his arms go up to intercept the punch after it already connected. He's unconscious as the follow-up right hand misses.

Also notice how little wind-up and how little the "winner" in this fight put on the initial left hand. Almost none. That was practically an "arm punch", and it was devastating because nig-nog didn't see it coming. If he did see it coming, some of the natural flinch reflex would've protected him a little bit, maybe.

not used to not getting the fight started by surprise. Unlike a real boxer these guys don't have thick skulls that can take a hit but that white dudes head was larger and likely has been hit by other guys many times so he doesn't wait for the fight to start since like there it could have been over in a single hit but he put his mark on it so the idiot would remember and fear that guy or others like him. He just sent a big message to the big talking guys that haven't met the big bad white boy before and what to expect. I think if it was 2 guys, would both be lying on their backs, with that guys testosterone and take no shit attitude.