Green’s Dictionary of Slang

(Aus.) to challenge someone to fight; thus excl. hop out! are you ready to fight?

1918		Kia Ora Coo-ee 15 June 4/2: Irate Lance-Jack: ‘Hop out the man who pinched my sock.’.
1919		C.H. Thorp Handful of Ausseys 272: Yer can ’op a Fritz out ter-morrer — yer so fond of inviting stouch.
1925		(con. WWI) Fraser & Gibbons Soldier and Sailor Words 120: Hop Out, To: To challenge anyone to fight.