Green’s Dictionary of Slang

(UK Und.) to beat; thus fagging n., a beating.

c.1698		implied in fag the fen
1719		A. Smith Lives of Most Notorious Highway-men, etc. (1926) 205: Fag, to beat. Fag the bloss, i.e., bang the wench.
1772		Bridges Burlesque Homer (3rd edn) 109: talthibious to the boats did run / To fetch for Jove a hot cross-bun; / Knowing their bones he’d soon be fagging / Should they not keep his chaps a wagging.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1809		G. Andrewes Dict. Sl. and Cant.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1834		‘Jack Downing’ Andrew Jackson 70: Gouge him, hoop his barrel, stranger; fag him in the craw, hit him in the pudding bag.
1859		Matsell Vocabulum.
1864, 1867, 1870		Hotten Sl. Dict.
1937–84		Partridge DSUE (1984) 374/1: fagging. A beating, thrashing, thumping.