1
general::
Phrase(s): play hardball (with someone)
Fig. to act strong and aggressive about an issue with someone. • Things are getting a little tough. The president has decided to play hardball on this issue. • If he wants to play hardball with us, we can play that way, too.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Act aggressively and ruthlessly, as in It's only a month before the election, and I'm sure they'll start to play hardball. This term originated in baseball, where it alludes to using the standard ball as opposed to the slightly larger and minimally softer ball of softball. It was transferred to describe aggressive behavior only in the 1970s.
American Heritage Idioms