Green’s Dictionary of Slang

a blow to the head, either with a fist or a weapon.

1785		Sessions Papers 6 Apr. 571/2: One of them said, damn his eyes, give him a topper at once .
c.1800		‘Drunk in the Night’ No. 26 Papers of Francis Place (1819) n.p.: I gave her a topper for making so bold.
1803		in Occasional Papers University Sydney Aus. Lang. Res. Centre (1980) No. 18. 44: He [...] had ‘knocked him down and given him a topper for luck!’ [OED].
1811		Lex. Balatronicum.
1818		W. Perry London Guide 79: [He] squared at him, — took him a topper, and a breast-cut.
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 177: Topper (a) — ring; a flush hit high on the upper works; applied also, to a blow with a stick on the head ; so ‘give him a topper for luck, and another for me.’.
1836		‘The Amorous Parson and the Farmer’s Wife’ in Comic Songster and Gentleman’s Private Cabinet 5: The parson’s fat gills grew quite pale at this news, / For he guess’d he should get a good topper.
a.1840		‘The Irish New Policeman’ in Henderson Victorian Street Ballads (1937) 38: I’ve just given him a topper for luck; and he’ll be quiet for the night I reckon.
1848		Bell’s Life in Sydney 12 Feb. 2/4: Allcott hit short, and received a ‘topper’ for the attempt.
1850		F.E. Smedley Frank Fairlegh (1878) 432: The topper as you’ve give Muster Richard ain’t done him no more harm, only lettin’ hout a little of his mad blood.
1866		Wild Boys of London I 42/2: The little ’un gave me a topper on the nut.
1873		Sl. Dict. 327: Topper a blow on the head. ‘Give him a topper and chance it,’ ‘let him have a topper for luck’ ― Pugilistic Slang.
1888		G.M. Fenn Dick o’ the Fens 274: Oh, how I should have liked to give him a topper with the pole!