A baseball bat is a smooth wooden or metal club

Club (weapon)

A club is among the simplest of all weapons. A club is essentially a short staff, or stick, usually made of wood, and wielded as a weapon since prehistoric times....

 used in the game of baseball

Baseball

Baseball is a bat-and-ball sport played between two teams of nine players each. The aim is to score runs by hitting a thrown ball with a bat and touching a series of four bases arranged at the corners of a ninety-foot diamond...

 to hit the ball after the ball is thrown by the pitcher

Pitcher

In baseball, the pitcher is the player who throwsthe baseball from the pitcher's mound toward the catcher to begin each play, with the goal of retiring a batter, who attempts to either make contact with the pitched ball or draw a walk. In the numbering system used to record defensive plays, the...

. It is no more than 2.75 inches in diameter at the thickest part and no more than 42 inches (1067 mm) in length. It typically weighs no more than 33 ounces (1 kg,), but it can be different from player to player. The batter swings the bat with two hands to try and hit a pitched ball fair

Fair ball

In baseball, a fair ball is a batted ball that entitles the batter to attempt to reach first base. In order for a batted ball to be fair, it must be hit in such a way that it:...

 so that he may become a runner, advance bases, and ultimately score a run or help preceding runners to score.
Although using a stick to hit a ball is a somewhat simple concept, the bat is a complex object.