Check out this video ... it opens with the two men arguing in the nosebleed section at Newark, New Jersey's Prudential Center. What sparked the confrontation is anyone's guess, but the man with his hair in a bun ("Bun Man") keeps calling the other guy a "white boy" and begging him -- "Slap me!" For the record ... both guys are white.

Anyway, "Bun Man" starts screaming, "C'mon!," while smacking himself in the face.

The other guy -- who's wearing a hat -- repeatedly asks "Bun Man" to "chill out," to no avail.

"Bun Man" gets right up in the other guy's grill pointing at his face and yelling more garbage.

Suddenly, the other guy snaps and punches "Bun Man" square in the head, knocking him backwards.

He follows up with a roundhouse to the face, causing "Bun Man" to tumble down rows of empty seats. Then he starts beating the crap out of "Bun Man" as people around them cheer and film the fight with their phones.

We don't know how this all ended or whether the cops were called or if anyone was injured. But we've reached out to the proper authorities for info.