Green’s Dictionary of Slang

to beat up; thus duffer n., a violent thug.

1870		Sportsman (London) 16 Apr. 4/1: A gentleman of the name James Murphy, otherwise ‘Jemmy the Duffer,’ was charged with assaults of the most unprovoked and brutal character on three women.
1943		R. Llewellyn None But the Lonely Heart 226: If he tried duffing my lamp, I’d set about duffing his. [Ibid.] 263: You blow the gaff about this, and I’ll come round here with the duffers and give the pair of you a right doing.
1951		R.A. Farran Jungle Chase 152: Duff him up when he is cheeky, give him a kind word when he does well and never treat him unjustly.
1967		P. Hall Harp That Once 119: So I got drunk, I quarrelled with my wife, I thumped somebody, perhaps I duffed up the Plastics King.
1971		J. Mandelkau Buttons 41: The coppers never made it back to their car. Both were duffed up.
1976		P. Theroux Family Arsenal 218: He’ll duff you up when he comes back. My daddy’s a good fighter.
1986		F. Taylor Auf Wiedersehen Pet Two 8: They duffed him up in front of his wife and bairns.
2000		Guardian G2 21 Mar. 4: He may have bragged that he could duff up Liam Gallagher in a boxing ring.
2001		OnLine Dict. of Playground Sl. 🌐 duff over, duff up v. to beat up. e.g. ‘let’s duff him over’.
2003		A. Coren Waiting for Jeffrey 11: You will have been duffed up so badly as to be left bleeding on a wonky hospital trolley waiting for the worst health service in Europe to get around to misdiagnosing you.
2006		Prison Slang Mommyblogger mydogharriet.blogspot.com 2 Mar. 🌐 You better be prepared to put up your fop-fops and duff that rustler out.
[2011		G. Hayward Corruption Officer [ebk] cap. 39: I was walking to my cell and this lil nigga just clocked me so I duffed him out].