Green’s Dictionary of Slang

(Aus.) a fight.

1919		Aussie (France) XIII Apr. 1/2: The driver hopped off the waggon and challenged the Sentry to a box-on. The Sentry threw down his rifle and bogged in, at the same time casting wild whoops into the air.
1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: box-on. A fight, a battle, a tussle.
1926		Register (Adelaide) 9 July 12/5: They heard some person call out ‘Yike’. His honor—What on earth does that mean? The public Solicitor—In good Australian, Your Honor, it means a ‘brawl’ or ‘box on’.
1968		S. Gore Holy Smoke 8: Here we are – around the time of the Israel-Philistine box-on, in the Holy Land.