Green’s Dictionary of Slang

(US) a gang-fight, incl. single-person combat.

1958		H. Ellison Web of the City (1983) 15: There was going to have to be a face-up soon, and he wasn’t sure he was man enough.
1968		J. Herndon Way It Spozed to Be (1970) 48: One kid flipped over the desks, a brief facing-up, that was all.