Green’s Dictionary of Slang

(Aus./N.Z.) a threepenny piece.

1893		Nat. Advocate (Bathurst, NSW) 20 May 2/4: If a ‘scrum’ is worth threepence what is a ‘kick’ worth ?
1897		W.T. Goodge ‘Great Aus. Slanguage’ in Baker Aus. Lang. (1945) 117: And his naming of the coinage / Is a mystery to some, / With his quid and half-a-caser / And his deener and his scrum.
1901		H. Lawson ‘Send Round the Hat’ in Roderick (1972) 472: The crown was worn thin as paper by the quids, half-quids, casers, half-casers, bobs and tanners or sprats — to say nothing of the scrums — that had been chucked into it in its time.
1911		Truth (Brisbane) 22 Jan. 6/4: [A]n honest business-man, who always pays twenty shillings in the pound, who would not take you down for a ‘scrum’.
1927		Smith’s Wkly (Sydney) 20 Aug. 11/2: Slanguage [...] Arithy. If hot dogs are a deaner a dozen at the fish and chip shop, and a bloke drifts in with ’arf a dollar in his kick, how many eats does he get? Answer to the nearest scrum.