Within softball, the bat is generally made out of hardwood, metal (aluminum), or composite materials (polymer arrangement usually of glass, carbon, and Kevlar fibers). International regulations dictate that a softball bat be no more than 34 in (86 cm) in length, 38 oz (1 kg) in weight, and 2.25 in (6 cm) in diameter. Bat speed is defined as how fast a bat moves through its arc when a softball batter swings it. It is generally determined at the bat's center-of-mass. The softball varies in size depending on the type of softball play. The International Softball Federation generally permits a ball to have a circumference of 11 in (28 cm) or 12 in (30 cm).
When swinging a bat at a softball thrown from the pitcher—either delivered at maximum speed with a flat arc, as in fast-pitch softball, or at slower speeds with an steeper arc, as in slow-pitch softball—the batter will either miss the ball or hit it. Hitting a softball is defined as striking a ball with a bat so that the ball lands in fair territory (either in the infield or the outfield) within a softball playing field.
In preparation for swinging a bat with a particular speed and hitting a softball, the batter will stand facing the pitcher inside a batter's box—either on the first-base side box for a left-handed hitting batter or on the third-base side box for a right-handed hitting batter. The bat is held with both hands near the handle-end while positioned over the shoulder and away from the pitcher. The batter hits the ball by
When a ball it hit by the batter within fair territory, it is designated as different terms depending on the result. A batted ball that is hit high in the air is generally called a fly ball. However, when a fly ball is hit at an angle greater than 45° (based on the angle between the horizontal ground and the ball's initial angle-of-flight), then it is considered a pop fly. A batted ball is called a line drive if it is hit into the infield at a height above the ground where an infielder could possibly catch it. However, a batted ball that hits the ground within the infield is considered a ground ball.
When swinging a bat to hit a softball, rotational (angular) mechanics rather than linear (straight-line) mechanics are primarily involved. Although the effects of gravity, airflow drag, and other minor considerations occur during swinging and hitting, there are two major forces acting on the bat to create bat speed. Angular momentum is the transfer of the body's rotational momentum to the bat that occurs when the hands are quickly swung in a circular arc. Angular momentum is generally defined as the cross-product of the position of an object and the linear momentum of the object.
Torque is the other major force and is the application of a rotational force at the bat's handle by the combined efforts of the hands, arms, and shoulders. Torque is generally defined as the force applied to an object multiplied by the distance from the axis of rotation to the point on which the force is acting.
When the path of the hands makes a circular arc as the batter's body rotates during the bat swing, the body's angular momentum is transferred to the bat in the form of accelerated motion (acceleration). This transference of momentum is generated as the arms swing the hands in a circular arc and as the barrel-end of the bat swings around the hands.
Torque is the result of two forces being applied to an object from opposite directions so that the object is forced to rotate about a point. Torque is applied to the barrel-end of the bat in the swing by the pushing and pulling actions of the forearms and hands.
To maximize bat speed, the softball batter must apply torque throughout the swing and maintain the hands in a circular path. In order to accomplish these actions most effectively, the upper body (shoulders, arms, and hands) should rotate around a fixed axis (the spine). For a well-hit bat, the collision occurs over a period of about one-thousandth of a second. The effect of this brief collision—that of the ball reversing direction—is brought on entirely because of the bat swing. The bat applies force to the ball, which compresses it, and the ball then exerts force on the bat upon regaining its original contours. The recoil action from this exerted force drives the ball quickly away from the bat. However, the recoil force is less than the compressive force because some of the collision energy is absorbed by frictional forces. In essence, a softball travels farther if it is struck by a bat that is swung faster.