A baseball bat is a smooth wooden or metal club used in the sport of baseball to hit the ball after it is thrown by the pitcher. By regulation it may be no more than 2.61 inches (6.6 cm) in diameter at the thickest part and no more than 42 inches (1.067 m) in length. Although historically bats approaching 3 pounds (1.4 kg) or 48 oz were used, modern bats of 33 ounces (0.94 kg) are common, topping out at 34 to 36 ounces (0.96 to 1.02 kg).
Baseball is a bat-and-ball sport played between two teams of nine players each, taking turns batting and fielding. The game occurs over the course of several plays, with each play beginning when a player on the fielding team, called the pitcher, throws a ball that a player on the batting team, called the batter, tries to hit with a bat. The objective of the offensive team (batting team) is to hit the ball into the field of play, away from the other team's players, allowing its players to run the bases, having them advance counter-clockwise around four bases to score what are called "runs". The objective of the defensive team (referred to as the fielding team) is to prevent batters from becoming runners, and to prevent runners advancing around the bases. A run is scored when a runner legally advances around the bases in order and touches home plate (the place where the player started as a batter).
The initial objective of the batting team is to have a player reach first base safely; this occurs either when the batter hits the ball and reaches first base before an opponent retrieves the ball and touches the base, or when the pitcher persists in throwing the ball out of the batter's reach. Players on the batting team who reach first base without being called "out" can attempt to advance to subsequent bases as a runner, either immediately or during teammates' turns batting. The fielding team tries to prevent runs by using the ball to get batters or runners "out", which forces them out of the field of play. The pitcher can get the batter out by throwing three pitches which result in strikes, while fielders can get the batter out by catching a batted ball before it touches the ground, and can get a runner out by tagging them with the ball while the runner is not touching a base.
Axial symmetry is symmetry around an axis or line (geometry). An object is said to be axially symmetric if its appearance is unchanged if transformed around an axis. The main types of axial symmetry are reflection symmetry and rotational symmetry (including circular symmetry for plane figures and cylindrical symmetry for surfaces of revolution). For example, a baseball bat (without trademark or other design), or a plain white tea saucer, looks the same if it is rotated by any angle about the line passing lengthwise through its center, so it is axially symmetric.
Axial symmetry can also be discrete with a fixed angle of rotation, 360°/n for n-fold symmetry.