In my article about how Gerrit Cole transformed himself, I talked about what things he changed with his spin rate, spin axis, and his pitch tunnel. Some of those words could be confusing to those who are new to learning sabermetric baseball, but today, I will be going in-depth with spin rate and spin efficiency first, and then next week I will explain more.
Spin rate is the stat that most people know about as it has become the staple analytic of pitch design. Measured in RPMs (rotations per minute), it is a factor in how much a pitch will move. An example to show how spin rate changes movement in a pitch is the fastball, the average RPMs for one in MLB is roughly 2,200. A pitcher who has above-average spin will make the pitch have more positive vertical break, or rise, on their fastball, compared to a pitcher who has a below-average spin rate whose will have less vertical break or will appear to drop more. It is the opposite for a curveball, in which the average RPMs for them are about 2,500, according to FiveThirtyEight. Above-average spin will lead to a more negative vertical break, or more drop, compared to the norm, and a below-average spin will lead to less break and will not drop as much. To show how spin rate affects movement would be to look at two different pitchers, one with a really high spin rate and one with a really low one. The two I will use in my example will be Justin Verlander, who has an average of 2577 RPMs on his average fastball, and Kyle Hendricks, an average 2044 RPMs on his, according to Baseball Savant. Their spin rates lead to this (Brooks Baseball):
The average four-seam movement (black) on Verlander’s fastball is almost 11 inches, compared to Hendricks, whose vertical break is about 8. This shows that spin rate helps fastballs get more lift to them, however there is another factor that decides how much a pitch will move. That factor is spin efficiency.
Spin efficiency is related to the spin axis of the ball and gives a ball its “true spin”. It comes from the idea that if you throw a ball in gyro-spin, or football spin, the spin will not affect the way the ball changes direction. If you throw a baseball in a gyro, it will have a 0% spin efficiency as it will not be affected by its spin. However, if you throw the baseball with it spinning exactly towards home plate, it will have a 100% spin efficiency. Here is a picture from Inside Pitch to show what the difference is:
The ball on the left spins over the top with a 100% spin efficiency, and the ball on the right is the gyro spin ball with 0% spin efficiency. As stated earlier, the amount of spin efficiency also leads to how much a pitch will move. To prove this, two pitchers with similar spin rates but different spin efficiencies need to be compared. We will stay with Justin Verlander’s high spin, but instead of Hendricks, we will use Mike Minor. Minor had an even higher spin rate than Verlander in his great 2019 at 2650 RPMs. These charts from Brooks Baseball will show the movements of all of their pitches, but focus on the four-seam (black) and take a guess of who had the higher spin efficiency.
As it shows on the charts, it is quite obvious that Verlander had a higher spin efficiency than Minor, with 98.5% to 67.8% respectively according to Baseball Savant. That 30.7% difference in efficiency lead to 3 more inches of break for Verlander, while Minor had almost the same vertical movement as Hendricks, even though his spin rate had 600 more RPMs. This shows that spin rate is not the only factor in pitch movement and that spin efficiency has a tremendous impact.
These two factors are huge in deciding how much a pitch will move for each given pitch type. It can lead to the situation between Minor and Hendricks if you can’t spin the ball efficiently and can lead to the Verlander and Hendricks example if you don’t spin your ball enough. However, just because a pitcher has a very good spin rate or spin efficiency, doesn’t mean that they are better than somebody else. All three of those guys are great pitchers who all use their arsenals extremely well. Pitchers must execute their pitches and sequence them well in order to have success.
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