Spin Axis is a metric widely used on pitch tracking technology to indicate how exactly a pitch is rotating during ball flight. This rotation is measured in 3 dimensions and can be visualized through the x-z plane and the x-y plane.
The x-z plane measures transverse spin and represents the plane perpendicular to the direction of the pitch’s flight. Put simply, this is the plane you see from the pitcher’s perspective as you look at the ball heading towards the plate.
The x-y plane measures gyroscopic spin, and represents the plane of the pitch you would see from a bird’s eye view looking down on the ball.
Spin Axis is a metric that helps explain why pitches move the way they do. The axis of a pitch directly impacts the type of spin you impart on the ball and this ultimately can determine how much movement your pitch experiences.
Measurement
Before we go any further, an important distinction to make is the difference between Spin Direction and Spin Axis. Spin Direction is simply the 2-dimensional representation of a pitched baseball.
In other words, Spin Direction describes the axis of rotation in 2 dimensions in strictly the x-z plane (Transverse), while Spin Axis represents a pitch’s axis of rotation in 3 planes using both the x-z (Transverse) and x-y planes (Gyroscopic). Therefore, Spin Axis is a more reliable measure because it incorporates both transverse and gyroscopic spin in its calculation.
When we’re analyzing the axis of rotation both Spin Direction and Spin Axis can have a different unit of measurement. Spin Direction is most commonly interpreted as time on a clock, where 12:00/6:00 represents backspin and topspin, and 3:00/9:00 signifies complete sidespin. Spin Axis on the other hand is commonly measured in degrees, where 180/360 degrees indicates backspin and topspin, and 90/270 degrees represents sidespin.
There are many factors that can affect your Spin Axis, such as grip, arm slot and release. These factors come together to create the orientation and type of spin your pitch experiences, which influences movement.
Summary
Spin Axis is a multi-layered pitching metric that is a key determinant of your pitch’s movement. Many other measurable metrics like Spin Direction, Spin Efficiency, and Horizontal/Vertical Movement are strongly correlated to spin axis, so make sure to check out our videos on those topics to gain a greater understanding of how they all come together to describe pitching performance.
Related Links
https://rapsodo.com/understanding-rapsodo-pitching-data-spin-profile/
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