Green’s Dictionary of Slang

1. to prepare oneself to fight, to give or accept a challenge.

1917		Register (Adelaide) 8 Feb. 9/4: Casey approached him and said:— ‘I’ll have you on.’ You are no gentleman’.
1921		Truth (Brisbane) 4 Sept. 3/1: [headline] ‘Who Won The Fight?’ A FRIEND BANGS A FRIEND ‘YES, YOUR ARE A — MONGREL AND I'LL HAVE YOU ON’.
1924		Goulburn Eve. Penny Post (NSW) 6 Dec. 8/3: [headline] I’LL HAVE YOU ON’ CR. O’BRIEN TALKS FIGHT Argument with Shire President Re Valuations.
1936		Cumberland Argus 7 Dec. 1/4: He entered the charge-room shouting out, ‘I’ll have you on: come out here, Clugston. Pull your coat off [...].’ He was in a fighting attitude.
1942		Barrier Miner (Broken Hills, NSW) 19 June 4/5: Time was when a lunch recess challenge —‘I’ll have you on after school’ — kept the entire school at fever heat all the afternoon.
1950		Recorder (Port Pirie, SA) 19 June 2/5: Street Fighters Fined [...] Hillyear was in the centre of the road ‘shaping up.’ Devlin called out: ‘Come on, I’ll have you on.’ Blows were exchanged.
1968		S. Gore Holy Smoke 13: I’ll have you on.

2. to attack physically.

1945

Baker Aus. Lang. 120: A man who attacks another is said [...] to have him on.