Green’s Dictionary of Slang

1. to attack using a blunt instrument; thus n. sapping,sap-up, a beating.

1911		B. Fisher Mutt & Jeff 19 July [synd. strip] Say! Do you realize you sapped me right on the bean.
1924		G. Henderson Keys to Crookdom 416: Sap up on. To beat, hit, slug, slough.
1925		G.H. Mullin Adventures of a Scholar Tramp 23: I was sapped by a yard dick. [Ibid.] 25: When a hobo receives a beating with a black-jack, he refers to it as getting sapped (the noun ‘sap’ means the instrument, not the beating).
1933		J. Spenser Limey 150: Castillo always did the ‘sapping’ (knocking out).
1940		R. Chandler Farewell, My Lovely (1949) 148: You’ve been sapped down twice, had your throat choked and been beaten half silly on the jaw with a gun barrel.
1941		‘Digg Mee’ ‘Observation Post’ in N.Y. Age 22 Feb. 10/5: [A]fter being the recipient of the well-known ‘sap-up’ [she] gladly and efficiently returned the compliment.
1941		Pittsburgh Courier (PA) 11 Jan. 7/1: Barbara Holt whose colored orbs were not the result of a sappin’ but walkin’ into a door.
1941		F. Swados House of Fury (1959) 114: ‘Go on, Bonnie!’ the girls cried [...] ‘Sap ’er up, oil ’er up!’.
1946		J. Evans Halo in Blood (1988) 100: Which one of you bastards sapped me?
1957		C. Himes Imabelle 50: Another cop let go his own prisoner and sapped the man about the head.
1957		R. Prather Always Leave ’Em Dying 94: It would help if you could check with those two guards and find out for sure who sapped me.
1965		C. Himes Rage in Harlem (1969) 52: [as 1957].
1966		C. Himes Run Man Run (1969) 57: I sapped him with my sap.
1971		R.D. Pharr S.R.O. (1998) 265: ‘If there’s any questions I’ll say you sapped me’.
1978		F. Norman Dead Butler Caper 59: There can be few worse ways of getting a splitting headache than being sapped by a novice. [Ibid.] 74: Isn’t sapped what they call it when you are struck over the head with a blunt instrument.
1981		H. Gould Fort Apache, The Bronx 285: Sergeant Clendennon was standing there, a blackjack dangling from his wrist. ‘You sapped me, Clendennon,’ Murphy yelled.
1996		H. Roth From Bondage 340: The fuckin’ railroad bull caught me ridin’ in the blinds [ ...] He sapped me silly, knocked the shit outta me.
2005		E. Weiner Big Boat to Bye-Bye 196: Even the toughest muscle boy looking to sap [...] you has got to think twice.
2023		(con. 1962) J. Ellroy Enchanters 101: I sapped him in the ribs and heard bones shear.

2. (US Und.) to hit with any implement, e.g. a whip.

1928

J. Callahan Man’s Grim Justice 64: I’m tired of being sapped [i.e. whipped] for not doing the task.