Last week, we talked about the first part of the basics of pitch design which was about spin rate and spin efficiency. In this part, I will talk about a pitch’s spin axis and how we believe it relates to the movement of the ball.
To start, spin axis is the direction of how a ball is spinning. The direction can be described numerically by the degrees it is spinning or by the direction it is spinning compared to the time on a clock (both pitcher’s perspective). This can be seen easier if I show you a picture of how the two work. The degrees picture is from Driveline Baseball and it shows what degree the ball would have compared to where it is spinning.
A fastball would, on average, be at 210 degrees of spin or at 1 on the clock, while a curveball would be at 360 or 0 degrees or at 6 o’clock. This spin axis goes along with how a ball moves, as a fastball typically moves in the direction of the 210 or 1 when it rises and has a little bit of arm-side movement, and a curveball will drop straight down when it is traveling as it is spinning down to the 360/0 or 6. This is also shown with sliders as the spin with a 90 or 9 o'clock spin axis and a change-up spins to the 270 or the 3 as they both have little vertical movement, but more horizontal movement. These numbers would be used for a righty, for a lefty you would just flip them around, so their fastball would be at 11 or 150, slider at 3 or 270, change-up at 9 or 90 and curveball still at 6 or 360/0.
To demonstrate this better, I will show you an example of a player’s arsenal and how they move. We will use Tampa Bay Rays pitcher Charlie Morton who just came off a fantastic year. In 2019 he threw a four-seamer, a sinker, a slider, a cutter, a splitter, and the nasty curveball that he is known for. The charts are from Brooks Baseball:
These show his curveball, fourseam, and slider movements with respect to the clock from the catcher’s perspective, so the clock is flipped side to side with the 9 in the 3 spot, the 11 in the 1 spot, and so on. His curveball moves about 10 inches horizontally and drops about 6 inches, compared to the clock his spin axis should be about 8 or 60 degrees, making this pitch more of a slurve than a true 12-6 curveball. The four-seamer has about 7 inches of vertical break with 9 inches of arm-side movement causing this pitch to have about a 1:45 on the clock or around 230 degrees on its axis. Finally, his slider doesn’t appear to move too much, this is due to its gyroscopic spin that we typically see on sliders. But, it does move about 2 inches horizontally and 0.5 vertically, this makes it about a 9:15 on the clock roughly 98 degrees on the axis. We can see if these numbers are correct with Brooks Baseball’s chart of Morton’s spin axis in terms of degrees:
The degrees we got with our degrees compared to the clock were correct. According to Brooks Baseball, Morton has an average spin axis of 61 degrees on his curveball and 229 degrees on his four-seamer. However, the slider was off by about 20 degrees, this may be due to how sliders typically have a gyro spin to it, so it will not show the true movement of the axis. The other two, though, show convincingly that spin axis has something to do with movement.
Spin axis is just one of the many resources we can use to try to build the best pitcher possible. This, combined with spin rate and spin efficiency are still just small pieces to the puzzle. Your guys still need to go out and command their pitches and compete every day in order to be successful. Without doing those thing, the pitchers will not perform well and all of the work put in will mean nothing.
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