Rapsodo Pitching Unit

During Part 1, we discussed the basics of pitch design.  For Part 2, we will dive into optimizing a pitcher’s fastball.  Prioritizing fastball optimization will always be the first thing we attack during the pitch design process.  Every other pitch will inevitably play off the fastball and the better your fastball is, the better the other pitches will play.  

Spin rate, spin efficiency, and spin axis all play vital roles in optimizing the fastball, so we’ll do a quick little overview before diving into each one independently.

Spin rate is the total spin imparted on the baseball by the pitcher.  For the most part, it seems raw spin rate is pretty individualized.  The only correlation to be seen across the board is that as the pitcher increases velocity, spin rate will increase as well. 

Spin efficiency tells us the amount of total spin being used to generate movement.  

  • The goal is to get the fastball to at least 95% spin efficiency. Anything less than that would be considered cutting the ball and not a true fastball.

Spin axis tells us what direction the spin is traveling from a pitcher’s point of view.  You can look at is as a clock, with a right-handed pitcher throwing over the top being 12:00, ¾ slot would be more 1:30, and side-arm at 3:00.  The closer to 12:00, the more the ball will use backspin and defy gravity.  

*Note-Left Handed Pitchers would still be at 12:00 for over the top, ¾ slot would be more 10:30, and side-arm at 9:00. (Exact Opposite of RHP)

Spin Rate

Let’s look at the 2019 Cy Young winner, Gerrit Cole, and see how an increase in spin rate paid massive dividends to overall performance.  During his time with the Pirates, he never produced a whiff rate above 20% on his fastball even though it was consistently above 95mph, which was well above league average.  During his final season with the Pirates in 2017, he averaged a 95.9mph fastball with a spin rate of 2154rpm.  That would be a Bauer Unit of 22.46. 

Bauer Units were discussed in Part 1 of the Pitch Design series and indicate whether a pitcher should pitch up or down in the zone based off their score.  Bauer Units can also tell us if a pitcher will be more inclined to get swing and misses on their fastball.  Anything below 24 (league average) would indicate less swing and misses on fastballs and that a pitcher should work down in the zone to induce groundballs.  So that would make since why Gerrit Cole threw with such high velocity but didn’t get many swing and misses.  


Fast-forward 2 years and some time with the Astros and everything has changed.  His whiff rate in 2019 was 37.5% on fastballs.  That is almost double in 2 years! Fastball increased by 1.2mph to 97.1mph in that same time frame but the big jump came in his spin rate, which is now averaging at 2530rpm.  That jump took him from a below-average Bauer Unit to an above-average one at 26.06.  

If we look at that from a performance standpoint:

  • ERA dropped from a 4.26 to a 2.60.
  • Strikeouts during season with fastballs increased from 87 to 178.
  • Batting average against fastball dropped over 100 points from 0.269 to 0.166.

This is just one example of how optimizing the fastball can pay huge dividends to overall performance.  There will always be other factors at play (which we will discuss further down) but it seems that the increase in spin rate elevated his fastball to another level.


Spin Efficiency

There seems to be a big misinterpretation of spin efficiency in the baseball world.  When looking at fastballs, spin efficiency can tell a coach/athlete how the fastball is coming out at release.  Look at it this way, as fastball spin efficiency decreases, the total amount of “true spin” impacting the baseball decreases, which in turn decreases movement.  This is true for both vertical and horizontal movement. The main reason for increasing spin efficiency is to allow for more MOVEMENT.

Original Tweet: https://twitter.com/BaseballFreak_9/status/1186078545652654081


  I’ll give you an example of an in-house athlete adjusting spin efficiency.  This athlete has a high spin-rate, so we were trying to increase his spin efficiency to maximize his vertical break.

Velocity (mph) Spin Rate (rpm) Spin Efficiency (%) True Spin Vertical Break (inches) Horizontal Break (inches)
91.6 2397 99.3 2380 22.1 7.0
92.9 2415 89.6 2165 18.3 8.5
91.4 2480 83.1 2061 16.2 9.3


Velocity wise, these three fastballs are pretty similar, but when you look into the other metrics, something pops out at you.  Even though the athlete had a higher spin rate on the 91.4mph fastball, it had less total movement than the less spinning 91.6mph because of the decrease in spin efficiency.  When just looking at velocity and spin rate, we would think that the 92.9mph fastball spinning at 2415rpm would have more overall movement than the 91.6mph fastball spinning at 2397rpm, but the lack of spin efficiency doesn’t allow the spin to be properly used.  The 91.6mph fastball captures the almost perfect spin efficiency and allows for the high spin rate to increase vertical break dramatically. 

All pitchers, regardless of spin rate, would want to maximize the spin efficiency to get as much movement on their fastball as possible.  We can use this knowledge to also impact how a pitcher uses his fastball.  High-spin rate pitchers would look more at maximizing vertical break and living up in the zone, while low-spin rate pitchers would look more at maximizing horizontal movement and live more down in the zone.  So now that we understand how spin rate and spin efficiency play off each other, there is one more attribute to the fastball that will tie everything together.  That attribute would be spin axis.  

Spin Axis 

So how does the spin axis play such a pivotal role in optimizing a fastball?   Spin axis will play a major role in how we use the spin rate and spin efficiency to optimize the athlete’s fastball.  For higher spin guys, we would look at trying to work the spin axis more toward 12:00 to increase that vertical break to defy gravity and make the fastball “ride”.

Original Tweet: https://twitter.com/ericjagers/status/1007253598777069570

With the axis closer to 12:00, we are creating as much true backspin on the baseball as we can while allowing the higher spin rate to work for the pitcher.  In contrast, guys who have lower spin rates would be more geared to try and create more horizontal movement by thinking of releasing it more ¾ quarter position (1:30 spin axis).  Left-handed pitchers would be looking at getting a spin axis closer to 10:30 to create horizontal movement (opposite of RHP).

Velocity (mph) Spin Rate (rpm) Spin Efficiency (%) True Spin Spin Axis Vertical Break (inches) Horizontal Break (inches)
89.3 2091 92.7 1938 00:56 15.6 8.9
89.7 2087 99.1 2068 1:06 16.3 11.0
89.8 2241 96.3 2158 1:08 18.1 12.6
88.1 2171 99.3 2155 1:10 18.4 13.1

Above is an example of an athlete we train who creates roughly league average spin on his fastball.  Averaging out the 4 fastballs’ velocity and spin rates, we can use the Bauer Unit conversion to see that this would be a league-average 24.  As pitchers, we want to be different from the next pitcher so being league average is not a good thing.  To differentiate from the norm, we attempted to change the spin axis to induce more horizontal break.  We can see that as the spin axis shifted even just the slightest bit, that it would induce an increase in horizontal movement.  We can also infer from looking back at spin rate and spin efficiency, that as the spin rate (or true spin) increased, so did the total movement profile of the pitch, including vertical break.

How Do We Impact Change

This is when it gets fun.  Once we have gained some data on an athlete, we can really look into making adjustments.  With spin rate being the only variable that seems to be inherent, we will look at the spin rate to adjust the spin efficiency and spin axis of the athlete’s fastball.  Understanding how these metrics affect each other can really benefit the coach/player and expedite the process of making adjustments.  Adjusting the spin efficiency and spin axis of the athlete’s fastball will be a trial and error process.  

Concerning spin efficiency, we understand that as it decreases, the pitcher is getting around the ball and not staying behind it through their delivery.  To try and fix this problem, we may try and tell the pitcher to overemphasize turning the ball over to mitigate some middle ground between being around the baseball and being on the inside of the baseball.  This neutral area in between is what we are looking for.  A lot of the time it helps to perform a movement pattern that is exaggerated to feel a different type of movement than what has been previously engrained for years.

If an athlete can’t really feel or understand what they are trying to accomplish, it becomes a lot more difficult to accomplish that goal.  Another strategy that I have found to be successful when dealing with pitchers who do not have very good spin efficiency numbers is to make them throw a fastball glove side and down.  To hit that low glove-side spot, the pitcher will need to stay on the baseball as long as possible and finish the pitch without pulling off to achieve the goal.  If he pulls off or “cuts” their fastball, it will dive off the plate, and if they release it early and don’t finish, it will end up in middle of the plate.  

With regard to spin axis, we understand that as the spin axis shifts from over the top (12:00) to side arm (3:00), vertical break will decrease, and horizontal break will increase.  We can use this information to our advantage.  Pitchers with higher spin rates would not want their spin axis to be 1:45 just like a lower spin rate pitcher would not want to be at 12:15 because it is not going to be optimizing how they could be using their fastball.  We want to be able to either maximize vertical or horizontal break and small changes in spin axis can pay huge dividends to that. 

We can manipulate spin axis in different ways, but it all goes back to trial and error once again.  We have to make that connection from the data and what result we want to produce and how can we help that athlete produce that result.  Coaches/pitchers can try manipulating wrist positions and a variety of different cues to try and achieve the desired result.  What works for one athlete may not work for another, so we need to have multiple available options ready at their disposal.

 Having the Rapsodo during bullpens is vital during this whole process.  High-speed cameras are also very beneficial in visualizing what is going on at pitch release and actually seeing what the pitcher’s hand is doing at release.  Intertwining the data with the player/coach really cannot be overlooked in how beneficial it is in helping expedite making significant changes. 

From pitch to pitch, we can analyze whether something worked better or worse and whether a certain “cue or feel” impacted the movement profile that we were going for.  If the adjustment works, we will try and reinforce it and challenge the pitcher to do it again and see if they can recreate the action and achieve the desired result.  In contrast, if something we try doesn’t work (and the data is backing it up), we can go ahead and chalk it up and try something else and not be hammering the same things over and over again. 

Future Research

For now, most tracking systems can only read magnus force on the baseball i.e. spin induced movement.  There is growing research on a new type of movement that can be induced by changing seam orientation.  Trevor Bauer has talked about his “laminar express” two-seam fastball that will take off arm side.  Stephen Strasburg has even found a changeup that seems to have the same affect but downwards. 

Gif courtesy of Pitching Ninja | Used for education purpose

Gif courtesy of MLB.com | Used for educational purpose

This “Seam-shifted Wake” can be applicable to two-seam fastballs, changeups, and possibly other pitchers.  Barton Smith is on the forefront of this research into baseball aerodynamics and he has some fascinating research at https://www.baseballaero.com/baseball-aerodynamics/

To try and summarize it, shifting the axis on certain pitches and orienting the seams of the baseball in certain areas will create a “Seam-Shifted Wake” that induces movement outside of the magnus force.  More research is still being done to see how consistently this can be done and how to go about implementing this new information into the pitch design process.  Nevertheless, this is fascinating new research and, if applicable, could give another edge to the pitcher.


As I hope you can now see, there is a lot that goes into optimizing the fastball and we still do not know everything.  Every pitcher will be unique and we have to figure out the best way to combine the different attributes mentioned above (spin rate, spin efficiency, and spin axis).  On the bright side, we do have way more readily available technology and data to work on these things now. 

We can manipulate what once was a bad fastball to possibly a great one with a few tweaks.  It is up to us to understand the data and what is going on and make the appropriate adjustments to maximize the player’s fastball and overall performance.

Part 3 of the pitch design process, we will really dive into Creating/Optimizing  Offspeed pitches based off their fastballs and will give examples for different situations.



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