1. You have to be willing to play hardball in the business world today If you aren’t aggressive, you’ll be taken over by the competition.
2. Mr. Norton had been mayor of a small town for many years, but when he decided to run for Congress his friends told him he would have to be prepared to play hardball. National politics can be much more aggressive than local politics.

The expression originates from the game of baseball, which uses a hard ball, as opposed to the similar game of softball.