Back to Basics: What is Spin Rate, Spin Efficiency, and Gyrospin?

Spin Rate

Spin rate describes how quickly a baseball rotates about an axis after it’s released. For example, the ball below has backspin and is rotating around the blue line. The spin rate would tell us how many revolutions the ball has around the line per minute.

Spin Efficiency

Spin efficiency is also important to understand, as it is more telling than simply looking at the spin rate of a pitch. It describes the percentage of the raw spin rate that directly impacts the pitch’s movement. For fastballs, change-ups and curveballs, the closer the spin efficiency is to 100% efficient the better. For sliders the ideal range in efficiency varies and will be discussed further later on.

Here is an example: Let’s say a a fourseam fastball has a spin rate of 1000 rpm and a spin efficiency of 90%. That means that 900 rpm out of the 1000 total rpm (90% x 1000) is contributing to the actual movement.

Gyrospin and Sliders

While spin rate is important for sliders, there is another type of spin that comes into play, gyrospin. The graphic above is measuring spin in two dimensions, but there is a third dimension that also must be considered when throwing the slider. It describes how the ball is spinning in and out of the page. A good representation of this is the visual below, which views the ball from the top. This time, we are looking at how the ball spins around the blue dot.

If this is difficult to visualize, picture a football with a perfect spiral. A baseball thrown like that would have pure gyrospin, and very little of the spin rate discussed previously would be contributing to the pitch’s movement.

What does spin tell us about sliders?

Generally speaking, there are two types of sliders: gyrosliders and sweeping sliders.

Gyrosliders typically have a spin efficiency between 0 and 25%, meaning very little of their spin rate actually contributes to their movement. They rely more on gryospin (football spin).

Sweeping sliders look like Frisbee sliders. Their spin efficiencies are higher than those of gyrosliders, but not as high as other pitch types that are ideally closer to 100% efficient. While gyrospin is still a factor for sweeping sliders, the two dimensional spin rate also comes into play, as it is contributing to the slider’s movement more than that of a gryoslider. This movement is typically horizontal break.