Green’s Dictionary of Slang

1. (gay) the dominant partner in male homosexual intercourse.

1971–2		C. Shafer ‘Catheads [...] and Cho-Cho Sticks’ in Abernethy Bounty of Texas (1990) 211: pitcher, n. – one of the two males in a homosexual act; acts as the male.
1988		H. Max Gay (S)language.
1999		J. Stahl Perv (2001) 305: Hey, Varnish, I’m a pitcher not a catcher.
2002		J. Lerner You Got Nothing Coming 30: Hey, hey, flaco! You a pitcher or a catcher, homes?

2. (US) a heterosexual male; spec. the male partner in heterosexual intercourse.

1983		R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].
2020		D. Winslow ‘Broken’ in Broken 3: ‘Jimmy’s a pitcher [...] but he prefers to play the field’.