Green’s Dictionary of Slang

a bottle or draft measure of Budweiser beer.

1993		G. Pelecanos Nick’s Trip 6: ‘What can I get you?’ she asked [. . . .] ‘I’ll have a Bud,’ [...] She pulled a long-neck from the cooler.
2000		J. Bouton Ball Four—the Final PItch 490: I don’t recall whether we pounded Bud or something else.