Spin-Rate and Spin-Direction

How quickly and what direction a baseball spins when it comes out of a pitcher’s hand is the driving force behind how a pitch moves. It directly influences the horizontal and vertical break of the pitch, and it’s caused by the pitcher’s arm-slot and hand position upon releasing the ball. 

The Magnus Effect

The Magnus Effect is the sole reason as to why the spin of the baseball is so important. The seams on a baseball create friction with the air around it when spinning, making it possible for pitches to move in different directions. Depending on the grip and position of the ball in a pitcher’s hand, the spin of the baseball will create pressure differences on each side of the ball. These differences will cause the pitch to break in the direction of lesser pressure. This is because one side of the ball spins towards the direction of travel, speeding up the airflow, and creating less pressure. The other side spins against the direction of travel slowing the airflow, and creating more pressure. 

Spin-rate

The speed at which a pitch rotates in the air, or spin-rate, is judged by rotations per minute (RPMs). Spin-rate is one of the most important factors that determine how a pitch moves. Spin-rate can be affected by how hard a pitcher is throwing, their grip on the ball, and hand position. It can also be affected by the physical strength of the pitcher. Spin-rate is tracked in the MLB by Hawk-Eye technology. 

Spin-rate is extremely important to how a pitch breaks. This is because the amount of pressure put on one side of the ball is affected by how quickly the ball is spinning in the air, which is directly proportional to how much the pitch breaks. This means a higher spin-rate will cause the break of a pitch to be more drastic, or ‘sharp’, when referring to breaking balls. 

Average RPMs for common pitch types in the MLB:

Fastball: 2200-2500

Curveball: 2500-3000

Slider: 2200-2600

Changeup: 1500-1800

Spin-Direction

Spin-direction is the measurement that tells pitchers which side of the ball will be affected by Magnus force. Put simply, spin-direction shows which direction the pitch will break. 

Spin direction is measured using numbers on a clock. For example, if a pitch’s spin direction is 12:00, it has perfect backspin. If a pitch has perfect forward spin, its spin-direction is 6:00. If a right-handed pitcher throws a pitch with perfect side-spin, its spin-direction is 3:00. 

For example, a fastball thrown with a spin-direction of 12:00 creates more pressure on the bottom of the ball, because the top of the ball is spinning in the direction in which the ball is traveling. This allows the pitch to fight gravity, forcing it to stay higher for longer, and making it more deceptive to the hitter. This phenomenon is referred to as ‘ride’. This same idea applies to pitches thrown at all spin-directions.