In baseball or softball, the pitcher is the player who throws the ball to the catcher in an attempt to strike out the batter. Another kind of pitcher is one that holds a liquid, like a pitcher of lemonade.
The pitcher is one of the most important players on a team, aiming the pitch so that it stays inside a certain "strike zone," but in a way that entices the batter to swing and miss or not to swing at all. The batter, on the other hand, tries to hit the ball that the pitcher throws, and maybe even to hit a home run. The 18th-century meaning of pitcher was "one who pitches hay into a wagon."