punch-out, n. — Green’s Dictionary of Slang

punch-out n.

(US) a fight.

1947		J.W. Arnold ‘The Lang. of Delinquent Boys’ in AS XXII:2 Apr. 122: Punch out [...] a fist fight.
1964		Male mag. in H.S. Thompson Hell’s Angels (1967) 72: ‘Listen, man, those beefs ain’t our fault,’ said a battle-scarred veteran of beer-hall punchouts.
1984		D. Jenkins Life Its Ownself (1985) 269: Memories [...] of punchouts and cussfights.
1989		Patriot News (Harrisburg, PA) 2 May A-17/1: They go out on the prowl. Anyone who spots a likely target can start the chant, ‘Punch-out, punch-out,’ which cues the designated puncher to sock the stranger as hard as he can.

punch-out artist (n.) [artist n. (1)]

(US) anyone who enjoys and is expert in beating up their opponents with their fists.

1966

H.S. Thompson Hell’s Angels (1967) 69: The Angels considered him a valuable hatchet man. ‘A punch-out artist is good to have around.’.