Green’s Dictionary of Slang

(N.Z.) a fist fight.

1961		B. Crump Hang On a Minute, Mate 165: And remember, Jack me boy, there’s no winners in a fight [...] A real mate isn’t going to judge you on how good you are in a knuckle-up.
1984		Partridge DSUE (8th edn).
2003		McGill Reed Dict. of N.Z. Sl. 124: knuckle-up A fist fight, probably barefisted. From mid C20.