“Hardball” is a no-nonsense attitude or approach to getting what you want in politics.
From the introduction to Hardball by Chris Matthews: “Let me define terms: hardball is clean, aggressive Machiavellian politics. It is the discipline of gaining and holding power, useful to any profession or undertaking, but practiced most openly and unashamedly in the world of public affairs.”
Example from All the President’s Men: “This is the hardest hardball that’s ever been played in this town. We all have to be very careful, in the office and out.”