Green’s Dictionary of Slang

1. (US tramp) to stay where one is for too long.

1927		‘Jargon of the Und.’ in DN V 447: Gaff, To stay at a place longer than is customary with tramps. ‘You been gaffin’ on that job like you was a gay cat.’.
1931		Irwin Amer. Tramp and Und. Sl. 82: Gaff— [...] To remain in any one place for too long a time.

2. (US tramp) to punish.

1931

Irwin Amer. Tramp and Und. Sl. 82: Gaff—To punish.

3. to be caught in the act.

1957

(con. 1943) A. Myrer Big War 131: You were gaffed.

4. (US campus) see stand the gaff under gaff n.²