Green’s Dictionary of Slang

(US) second-raters, underdogs.

1960		J. Brosnan Long Season 67: Nobody pitched a complete game all spring, except me. Against the Yankee "B" team, most of whom are now at Richmond in the international [i.e. minor] league.
2014		Ruderman & Laker Busted 88: We were the underdogs. The B team. The long shot. We weren’t expected to win.
2022		A. Kirzman Giuliani 361: The cast of characters, with their hyperventilating language and sloppy arguments, screamed B-team .