If someone plays hardball, they will do anything that is necessary to achieve or get what they want, even if this involves being harsh or unfair.

Do not play hardball meaning?

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.

What is hardball slang for?

play hardball, to act or work aggressively, competitively, or ruthlessly, as in business or politics.