foul ball, n. — Green’s Dictionary of Slang

foul ball n.

[baseball jargon foul ball, a ball struck so that it falls outside the lines drawn from the home base through the first and third bases]

(US)

1. an unpleasant, poss. criminal character.

1919		A. Baer Flapping Over New Leaves 4 Jan. [synd. col.] Look at the kaiser. He knows that he is a foul ball.
1925		T.A. Dorgan in Zwilling TAD Lex. (1993) 37: He eats bananas skins and all. Oh, he’s just a foul ball.
1935		F. Wead Ceiling Zero Act II: When you came along I was a foul ball.
1941		S.F. Chronicle 1 June H5/7: When it comes down to brass tacks the most polished orator will lapse into [...] ‘stymied,’ ‘foul ball’ and other expressions borrowed from sports.
1950		J.T. Farrell ‘Milly and the Porker’ in Amer. Dream Girl (1950) 197: He may be nothin’ but a measly foul ball, but he’s got your number.
1960		G. Swarthout Where the Boys Are 3: He needs some flesh for Friday night, no foul balls, nothing too brainy, all queens and amenable.
1962		T. Berger Reinhart in Love (1963) 98: The present client is the black sheep, the foul ball, of the moneybags clan.
1976		C. Keane Hunter 140: The Branch brothers were total foul-balls.
1982		T. Considine Lang. of Sport n.p.: Finally asked the uninvited guest, a real foul ball, to leave [R].

2. a distasteful statement.

1991

W. Adler Immaculate Deception 96: That’s a foul ball, FitzGerald, a real foul ball.