Spin Efficiency (aka True Spin) measures the amount of spin that contributes to a pitch’s movement.
Both terms define the same measurement, but are displayed in two different formats. True spin is the raw value, for example: 1500 rpms. While Spin Efficiency is represented by a percentage, and is calculated by dividing the true spin by the total spin rate. For example, 1500 true spin divided by a 2000 total spin rate results in a 75% spin efficiency.
Application
To determine a pitch’s Spin Efficiency, we’ll first need to understand the difference between gyro and transverse spin.
A ball thrown with 100% spin efficiency has complete transverse spin. This means it has straight backspin, sidespin or topspin. This type of spin uses its rotation to maximize magnus force in order to create “spin induced movement.” Fastballs, curveballs and changeups are pitches that usually contain a high degree of transverse spin.
Examples
For example, if you’re looking to maximize vertical movement on your four-seam fastball you’ll want to be as close to 100% spin efficiency as possible. A 100% spin efficiency means you’re using perfect backspin to maximize spin induced force onto the ball which leads to “lift” during ball flight.
Conversely, a pitch thrown with a 0% spin efficiency will rotate with gyro spin, similarly to a bullet or a football spiral. This type of spin possesses little to no magnus force so it will not create any “spin induced movement.” The drop that you see on pitches with small amounts of spin efficiency will be mostly due to gravity or other aerodynamic factors.
For example, if you’re looking to create a gyro slider, striving for less than a 10% spin efficiency is a great target range. This is a pitch type that relies on little spin induced movement and mostly gravity to be effective.
Summary
Spin Efficiency helps us understand the movement profile of different pitches. It is not like velocity, where the higher the number the better off you are. It’s all about how you plan to employ the pitch.
Most pitches will vary in spin efficiency, so, it’s important to understand how your metrics lead to your desired strategy for a given pitch type and ultimately, its respective movement profile.
You can find spin efficiency using technology such as Rapsodo. If you want to compare your spin efficiency with the likes of your favorite Major Leaguers, you can find those numbers on baseballsavant.com, displayed as ‘active spin.’
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