Green’s Dictionary of Slang

(Aus.) an altercation.

1899		Arrow (Sydney) 4 Nov. n.p.: [headline] ‘SCRAPPO.’ / The Sydney ‘Bulletin,’ in the course of a scurrilous attack on the ‘Sydney Times’ [...] expressed its disapproval of the contents of the ‘Times’ .
1935		L. Lower in Aus. Women’s Wkly 5 Oct. 11/1: [headline] WHEN LOWERIO Met the Italio ... What a SCRAPPO! / Oh, Musso! My Trade Missiono Ended in a Terrific Rioto .