Green’s Dictionary of Slang

(US) aggressive, intimidatory.

1978		H.R. Haldeman Ends of Power 5: Chuck Colson had become the President’s personal ‘hit man’; his impresario of ‘hard ball’ politics.
1986		J. Ellroy Silent Terror 275: If my destiny is to become a prototypical hardball homicide cop, so be it.
1990		(con. c.1970) G. Hasford Phantom Blooper 30: It’s a hardball world and Communist aggression must be defeated at any price.
2000		C. Cook Robbers (2001) 35: Play hardball politics all week, rise above it on Sunday.
2000		Indep. Rev. 6 Jan. 13: This yarn about a hardball newspaper man and a small-town tease.
2017		T. Pluck Bad Boy Boogie [ebook] ‘You think this is hrdball [...] This isn’t even close’.
2022		G.M. Graff Watergate 296: [Tip O’Neill] had witnessed plenty of hardball politics and thought he knew the world of dirty tricks inside and out .