Green’s Dictionary of Slang

1. to become feeble, to collapse, to give way, to break down; thus crock off, to die.

1928		R. Hall Well of Loneliness (1976) 181: I’d nowhere to turn and my health was crocking.
1929		(con. 1916) F. Manning Her Privates We (1986) 90: If you crock up, you will only be a damned nuisance.
1937–84		Partridge DSUE (1984) 270/2: from ca. 1890.
1940		A.P. Herbert Let Us Be Glum (1941) 14: Sock the Wops and knock their blocks / Sock the Wop until he crocks.
1957		(con. 1944) A. Myrer Big War 286: He may crock off, though. He lost enough blood to float a boat.

2. (US) to hit on the head, to injure.

1919		S. Graham A Private in the Guards 68: The object of the N.C.O.’s seemed to be to ‘crock him up.’.
1926		Boys’ Realm 16 Jan. 264: It was one thing to suggest crocking Harry, and another thing to do it.
1930		(con. 1910s) D. Mackenzie Hell’s Kitchen 181: He had been boxing with a corporal [...] and had crocked his thumb badly.
1940		R. Chandler Farewell, My Lovely (1949) 203: I crocked the orderly with a bed spring.
1948		J. Archibald ‘Photo Finish for a Dame’ in Popular Detective Mar. 🌐 He [...] threw it [i.e. a camera] toward the bar where it crocked a character who had just downed one neat.
1968		G. Slatter Pagan Game (1969) 28: I might’ve made it if I hadn’t crocked my knee.