Understanding Rapsodo Pitching Data: Spin Profile

There are two release measurements that affect the overall movement profile of a given pitch: spin direction and gyro degree. While both are measured at release, we will tackle each measurement within their own dedicated sections. 

Spin Direction 

Originally listed as spin axis in earlier iterations of our technology, Rapsodo measures spin direction by reading the direction the seams are traveling as the pitcher releases the ball; these measurements are converted to resemble the hands on a clock. The direction of the ball should be read as where the hour hand on a clock is pointing for the given time listed.  

The directions will vary both based on pitch type and pitcher handedness. Left-handed fastballs and changeups typically fall between 10:00 and 12:00, while right-handed fastballs are usually between 12:00 and 2:00; in all cases, 12:00 indicates exact backspin. Curveballs, due to their topspin profile, are typically thrown between 4:00 and 6:00 for lefthanders and 8:00 and 6:00 for righthanders; similar to fastballs, 6:00 represents exact topspin. 9:00 and 3:00 represent exact sidespin for each respective handedness and are generally seen in sweeping breaking pitches. Sliders, due to their bullet spin profiles, will typically fall close to 12:00 for both righthanders and lefthanders, depending on specific classification (gyro, topspin, or sidespin).

Gyro Degree 

Depending on a combination of a pitcher’s natural arm slot, ability, and the desired movement profile, subtle changes in spin direction can vastly change the shape and look of a pitch. This is where gyro degree comes into play. The easiest way to explain gyro degree is as a measurement that tells us how well a pitcher stays behind the baseball at release, measured on a radial scale between 0-90°. 0° marks pure transverse spin, while 90° is pure gyroscopic (bullet/football spiral) spin. In most cases, left-handed pitchers will spin their pitches with a negative gyro degree, while right-handers will be positive. If spin direction remains constant, an increase or decrease in gyro degree will decrease or increase spin efficiency (more on this later), respectively. To better illustrate gyro degree, let’s take a look different pitch types and their profiles: 

Fastball 

As shown by his spin direction and 99.6% spin efficiency, Pitcher A throws his fastball with much more backspin than Pitcher B. By staying square behind the ball (indicated by his single-digit gyro degree), Pitcher A is able to maximize how powerfully the ball resists the pull of gravity, noted by the 23 inches of vertical break (i.e. ride). 

Pitcher B throws his fastball with a spin direction much more common in ¾ slot pitchers, which already puts the pitch in a position to be affected differently by gravity than Pitcher A’s fastball. However, he spins the ball with a gyro degree that is more off-center than Pitcher A, lowering his spin efficiency and increasing the ball’s induced horizontal movement (i.e. run) and vertical drop (i.e. sink). 

By looking at the above chart, you should be able to deduce that Pitcher A will have success throwing his fastball in the upper third of the strike zone and higher, while Pitcher B will benefit from keeping his fastball at the bottom third of the zone and lower. If Pitcher A’s fastball spun with the same gyro degree as Pitcher B’s fastball, the effect Pitcher A’s natural arm slot and spin direction on the movement of the pitch would have been minimized, lowering his induced vertical break and making his fastball less effective. Conversely, if Pitcher B stayed behind the ball a bit more squarely, his ball would not sink and run as desired, leaving it up and susceptible to finding barrels.

Curveball 

In this scenario, Pitcher A throws a slurve and Pitcher B throws a more of a 12-6 curveball. By spinning the ball with almost even amounts of transverse spin and gyroscopic spin, Pitcher A generates only a slight amount of two-plane break. Since this pitcher is above the MLB average gyro degree for slurves (30-40°), he is limiting the amount of total break he can put on the ball; in this case, you would want to have the pitcher attempt to stay through the ball more in order to increase spin-induced break. 

We see an example of what effect reducing gyro degree can do for a breaking ball in Pitcher B’s curveball. Though both pitchers throw their curveballs with similar off-center spin directions and high spin rates, Pitcher B generates much higher break measurements by keeping gyro degree at a minimum. This allows Pitcher B’s natural ability to spin a breaking ball have more influence on the flight of the ball, exemplified by his high vertical break measurement.

Changeup 

Since they are meant to most closely resemble a pitcher’s primary fastball, one could posit that changeup spin profiles should also be relatively similar to those same fastballs. However, the desired movement profile and pitcher’s feel for the pitch play a large role in changeup selection. Pitcher A in this example is the same Pitcher A from the fastball example earlier. Notice that his spin direction and gyro degree are quite different from his fastball; despite these differences, he is able to greatly reduce the amount of induced vertical break on this pitch while vastly increasing horizontal break, giving him much more fade than what most would have expected out of pitchers with “rising” fastballs. 

Pitcher B delivers a traditional straight changeup (listed as a three-finger changeup in our MLB Data Guide). His changeup’s spin direction and gyro degree are extremely similar to his fastball, so he primarily relies on velocity differential to keep hitters off balance. While velocity separation is key in all offspeed offerings, Pitcher B would benefit from increasing the gyro degree on this pitch and perhaps even a slight spin direction adjustment in order to generate more movement off his fastball.