HardBall! places you in the position of a big league manager and player. You'll choose to play as either the All Stars or the Champs. Each team has its own roster of fictional players with varying batting averages and pitching ERAs. If a player has a higher batting average, he is more likely to get a hit and, in some cases, a home run if he has sufficient power. Along with choosing your team, you can also decide whether to play as the visitors or the home team.
Games can be played against the computer or a friend (the defense uses a joystick while the offense uses the keyboard). On offense, you can pinch hit or run with players on the bench, and defensive minded coaches can bring in a relief pitcher or substitute fielders at any time.
When pitching you can choose to throw one of eight pitches: Fastball! (straight and very fast), Fastball (straight and fast), Offspeed (straight), Change-up (slower straight pitch), Curve Ball, Screwball (opposite of curve ball), Sinker (the ball drops and curves down), and Slider (similar to a curve ball, but breaks at the last moment). Once the ball is hit, you will be able to control only the player that is nearest to the ball. You can then catch the ball and throw it to any of the bases in the infield.
The At Bat or Offense parameters of HardBall! allow you to choose which direction to swing your bat (i.e., swing high, low, or outside). While running the base paths, you can also decide whether to stop or advance to the next base. You also have the option to steal a base or bunt to move the runners into scoring position.