Green’s Dictionary of Slang

baseball n.

(US prison) homsexuality; a homosexual relationship.

[US]D. Winslow Border [ebook] No ‘baseball’ — homo shit.

SE in sl. use

In compounds

baseball Annie (n.)

(US) amongst baseball players, a female camp-follower, a groupie.

[US]J. Bouton Ball Four 218: A stew can come under the heading of class stuff [...] in comparison with some of the [...] camp-followers or celebrity-fuckers, called Baseball Annies.