Baseball Spin Axis, Spin Rate, Spin Efficiency Explained

baseball spin axis

We’ve all heard it, “pitching wins games”.  Well, some pitchers are about to win a lot more games. For eons, pitching coaches have talked about mechanics, command and control.  Then came velocity and threw out all the old adages and wrecked the house.  Today, it seems like everyone wants velo first, and then everything else as well.  I am here to say that things are about to change again!  The advent of equipment like the Rapsodo Pitching camera and all the talk about baseball spin axis and spin rate is changing the game and doing it fast.

All this new information is giving coaches new insights that only data analytics can bring.  Eyes don’t see everything, especially at high speeds.  I can say this without a doubt because I have seen it firsthand.  You notice something on a pitch, and then you get the data and realize you were wrong.  Then you look at high speed video and it agrees with the data.  That’s the reality of present day.

I also know there are coaches and pitchers out there that have already jumped all over this and are winning more games because of it.  Just ask Trevor Bauer.  But, at the moment they are far and few in between.  Having said that, I believe it’s all about to change and those that learn and adopt the new technology will rise to the top of the game.

The new information isn’t necessarily going to help you throw harder and it can’t make you throw strikes.  You still have to continue to train and prepare for all those things.  However, the information can be used to help pitchers become better at their craft.  And I don’t mean just better, I mean “a lot” better.

Most folks are calling this “pitch design”.  Seems like a worthy name, but it’s just as much about refinement and development as it is about design.  To me the word “Design” implies a plan to show the function of something before it’s assembled.  I believe, first and foremost, this new area is about pitch refinement and improvement, and then design.  We can design new pitches all day long, but first let’s evaluate a pitcher’s existing stuff and see where he can improve.  Let me say this with a megaphone…

Pitchers and coaches that study and learn about this new undiscovered country and incorporate it into their training programs will make themselves better at their craft and win more games.

A few years ago we purchased a Rapsodo Pitching camera system.  Honestly, we had no idea how it worked.  The information coming out of it was overwhelming and confusing.  Although some of this information has been available to varying degrees in the pro ranks, there was no pre-existing playbook or manual on ball movement.  So, our pitching coach Robbie Aviles and I dug in.  Robbie previously a RHP with the Cleveland Indians for seven years brought the in-depth pitching knowledge and given my engineering degree from 30 years ago, I quickly learned the science and physics behind it.  Together, over a few months, we hacked the code.

Pitching coaches talk about movement often.  We’ve all heard it, but until recently it was based on what coaches could see with their eyes.  Unfortunately, the eyes only give you a small piece of the story.  For example, for a pitching coach, a 4-seam and 2-seam might look like they are moving just fine.  But our data shows that 9 out of 10 pitchers’ 4-seams and 2-seams move with little to no differentiation.  Yup!  They’re basically the same pitch, even though they’re gripped differently.  It’s really no one’s fault.  A pitcher can’t throw both pitches at the same time, so comparing them previously was impossible.  Until now!

So, with all that said, let’s get into it.  This article is a bit of a crash course on the science of ball movement (also commonly referred to as the “break”).  It’s the type of article you would have previously seen in sabermetrics journals, but times are changing, and all those topics are coming into the mainstream.  So, buckle up your seat belts.  I have simplified things a bit, but you may have to read it twice anyway.  The basic concepts and terms that I am about to review are just as important as velo and mechanics and they’re all about what I call the “point of release”.

Basic Concepts and Terms

In order to understand pitching data, you need to have a good understanding of a few basic concepts, including:

    • Ball Movement
    • Magnus Force
    • Different Types of Spin
    • Gyro Spin
    • Baseball Spin Axis
    • True Spin and Spin Efficiency

Ball Movement

A deviation from a baseball’s trajectory from the time it’s released until it crosses Homeplate.  This deviation or movement is mathematically measured against a “hypothetical” pitch (we call a gyro ball) that doesn’t move at all.  Here is an image that should help explain it a little better.

baseball spin axis

Magnus Force

A baseball on its way to Homeplate is exposed to difference forces tugging at it, all of which are competing to change its trajectory. To put it simply, these forces include gravity, air resistance, and the velocity with which it was thrown.  However, it’s also impacted by what’s called the Magnus Force.

Magnus Force is basically what creates the deviation from a baseball’s expected path by creating what everyone refers to as “movement”.  It is a phenomenon associated with a spinning baseball that drags air faster towards one side as it reaches Homeplate.  This in turn creates a difference in pressure that moves the baseball in the direction of the lower-pressure side.  For example, the backspin of a fastball:

    • Increases air pressure under the ball
    • Reduces air pressure above the ball
    • Creates a Magnus Force that puts an upward movement pressure on the ball

Don’t misunderstand me, the ball still falls due to gravity.  It just falls a little slower.

Different Types of Spin

A baseball on its way to Homeplate can spin along all 3 different axes (x- y- or z-axis) at any given moment.

These different types of spin, each have their own impact on ball movement:

    1. Z-axis: Lateral ball movement, side-to-side along the z-axis
    2. X-axis: Up or down movement, topspin or backspin along the x-axis
    3. Y-axis: Gyro spin, like a football, along the y-axis (between catcher and pitcher).  Gyro spin generates NO movement (reviewed below)

A baseball could spin along one or all three axes at the same time and its ultimate direction of movement is dependent on the net amount of spin along the three axes.  Although, rarely is a baseball spinning 100% along a single axis, the images below provide a visual of each specific type of spin along each axis (in red):

baseball spin axis

Gyro Spin

t might surprise you, but all spin is not alike, as some of the spin creates movement and some of it doesn’t.  For example, in the image above:

    1. The baseball on the left spinning along the vertical dashed red line, will have movement to the left or right, as Magnus Force pulls it in one direction or the other
    2. The baseball in the middle, will have movement up or down
    3. The baseball on the right (with gyro spin), will have NO Magnus Force and NO “movement” in any particular direction

Baseball Spin Axis (simplified)

Although a baseball could be spinning in multiple directions at one time, generally, one of those directions is the most dominant and where the net amount of Magnus Force will direct the ball.  Measuring the axis of the ball along that direction is what’s referred to as the Baseball Spin Axis.  If you remember nothing else from this article, remember this:

Spin axis, or tilt as some call it, is 100% correlated with the direction of ball movement. If you want to move the ball in a certain direction you have to tilt the spin axis in that direction.  Learning how to shape the baseball spin axis is the essence of pitch design.

spin axis

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True (Useful) Spin and Spin Efficiency

True Spin reflects only the components of spin that contribute to movement (basically A and B only).  For example, in simple terms, a fastball may have a total spin rate of 2,000 rpm along all 3 different axes.  However, if 500 rpm of that total is gyro spin (y-axis), we remove that component to get a True Spin of 1,500 rpm.

This is also sometimes listed as Spin Efficiency % which in this case would be 75% (1,500 / 2,000).  These are simply measurements of the amount of spin that contributes to a ball’s movement.  Here is an image that might clarify things a bit:

gyro spin

Having said that, I should also say that different types of pitches are expected to have different percentages of Spin Efficiency.  A high percentage isn’t necessarily bad or good.  Certain pitch types are expected to have a high percentage, while others are expected to have a lot less.  For example, a typical MLB fastball will likely have a Spin Efficiency of 95-100%, while a slider might be in the 20-35% range.

Where Does the Amount and Direction of Movement Come From?

With all the basics behind us, now let’s go over where ball movement specifically comes from. There are two major components to ball movement, the amount of movement and the direction of movement.  Here are the contributors to each:

    • Amount of movement (“break”)
      • Velocity
      • Amount of True Spin
    • Direction of movement
      • Spin Axis

If you spend enough time watching high speed video from the point of release, you’ll realize that baseball spin axis is highly correlated with the initial grip, the finger placement and pressure points on the ball at the point of release.  Arm slot, elbow flexion and wrist position also play a role, but the final point of contact with the fingers mostly shapes the ultimate spin axis at the point of release.  If you don’t believe me watch some high-speed video.

4-seam Fastball Example – Now, as an example, let’s review a typical 4-seam fastball pitch from a righty pitcher’s viewpoint with the following metrics:

    • Pitch Type: 4-seam FB
    • Velo: 82.4 mph
    • Total Spin (x- y- and z-axes): 1,959 rpm
    • True Spin (x- and z-axes only): 1,806 rpm
    • Spin Efficiency (True Spin / Total Spin): 92%
    • Horizontal Break: +9.4” vs. dead center on movement chart below
    • Vertical Break: +17.1” vs. dead center on movement chart below
    • Baseball Spin Axis: 00:58 minutes (just shy of 1 o’clock)

Strike Zones vs. Movement Charts – The following charts demonstrate a strike zone and a movement chart side-by-side.  These two are often confused.  The chart on the left is what we’ve all seen many times.  The chart on the right is about ball movement-only.  Said differently, it explains how the ball moves vs. a hypothetical gyro ball (black dot) at dead center of the chart.  It has nothing to do with strike zone on the left.

Basically, this baseball crossed the plate in the lower right-hand corner of the strike zone (left), but it moved up and in on a righty pitcher, 9.4” horizontally and 17.1” vertically (right).

Now let’s overlay them a little and try to make more sense of it.  For comparison, the charts below show the movement in dashed blue line on both charts for clarification.  As you can see, without the movement this ball would have ended below the strike zone.

What is Relative Pitch Movement?

A lot of pitching folks talk about the real value in pitching data to be in the spin rate numbers. You often hear so and so has a curveball with a 3,000-rpm spin rate, or a fastball with 2,800 rpm spin rate.  I totally disagree.  Although it’s all great info, I believe that the most relevant information in the data is in the movement numbers and the spin axis. When you look at how elite pitchers move the ball, you quickly realize that their success is as much in their ability to tunnel pitches and move the ball well, as anything else.

The chart we reviewed earlier is a typical pattern for a 4-seam fastball coming from a righty pitcher, up and in.  Now, let’s look at a dozen elite MLB pitchers collectively and how they move their various pitches.  You can see why they’re elite.

These guys move the ball exceptionally well.  This gives them the ability to “tunnel” their pitches with great deception.  The best pitchers have very distinct pitch movement patterns from pitch-to-pitch.  I call this “Relative Movement” and if you want to go far in this craft you should work towards creating similarly distinct movement patterns from pitch-to-pitch.

I am willing to bet that at the highest levels of the game, the teams with the most advanced data analytics efforts, are training their pitchers to not only separate their movement patterns but telling them exactly where they want a certain pitch to hit on the movement chart. Why you ask? Because they already know hitters have difficulty with that type of movement. Think about that for a second and let it sink in!

The punch line here is that movement is the result of everything that comes before it.  If you don’t know “why” and “how” your various pitches are moving, then you might want to learn and find out.  I guarantee that you can refine and further develop your pitches and even design new ones.  How? That will require another few thousand words.

Interested in learning more about ball movement and pitch design, click here!

Note: This article was published in the July/August 2019 issue of Inside Pitch Magazine (Official Magazine of ABCA). By Bahram Shirazi (BSEE, MBA, Co-owner RPP)

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