Over the last decade of baseball there has been an explosion in the use of technology and analytics to define or redefine the game as we know it.  Along with this growth has come, what seems like, a whole new language that coaches are having to learn in order to communicate with the modern player.  This blog series is aimed at simplifying some of this language to hopefully create a bridge between those that consider themselves “old school” and the “new age” coaches who have adapted and learned this new language.

In the simplest of terms, Spin Rate is the how fast the ball is spinning as the pitcher releases the pitch.  When a pitch is thrown, there are many factors that go into how it moves, how it creates shape and how a hitter will potentially react to it once it enters the zone.  Modern coaches use tracking technology like Rapsodo or Trackman to measure this spin in revolutions per minute or RPM along with defining how useful that spin is in creating the desired pitch.

The Magnus Effect was first discovered by Sir Isaac Newton in 1672 and later expanded by its namesake Heinrich Gustav Magnus in 1852 as he attempted to describe why cannonballs curved in flight.  The basic principle of the Magnus Effect says that the object will be deflected from its path based on the direction the object is spinning and the difference in air pressure on either side of the object created by the spin.  For example, objects with top spin will create downward pressure and thus downward movement (Think Curveball) while objects with backspin will create upward pressure and thus upward movement (Think Fastball).  There are additional forces at play that will define overall movement and we will get into those in future articles.

You don’t have to be a scientist or a “nerd” to understand the simplicity of spin rate.  As a ball is released from the hand it has the potential to spin in 3 different directions.  The X Axis is simply defined as the left-right spin and vice versa.  The Z Axis is simply defined as top-bottom spin and vice versa.  The Y Axis is simply defined as gyroscopic spin.  An easy way to think of gyroscopic spin is to imagine throwing a football towards the catcher and defining the direction the football is spinning.  The images below attempt to help visualize how a ball spins as it is released in relation to the terms used to define that spin.

Key Points To Remember:

• X Axis = Left and Right Spin
• Z Axis = Top and Bottom Spin
• Y Axis = Football Spin

Depending on the pitch type thrown there are more desirable spin directions and speeds that must be understood.  There are two types of spin that are created when throwing a baseball.  There is “useful spin” which Alan Nathan describes as “transverse” spin and “gyroscopic spin” which we defined earlier.  Transverse or “useful spin” directly influences ball movement and on most pitch types, is a desirable characteristic.  Gyroscopic spin has little to no influence on ball movement and is thus a less desirable characteristic on most pitch types.  We will discuss where it can be useful in a second.

Key Points To Remember:

• Transverse Spin (Useful Spin) = Direct Influence On Ball Movement
• Gyroscopic Spin (Not Useful) = No Influence On Ball Movement (Useless)

Now that we understand the concept of spin rate and the direction the ball can spin, let’s talk about how we determine how efficient a thrown ball is spinning.  When a device like Rapsodo and Trackman measures a ball’s spin rate it gives us two readings that we should be aware of:  overall spin rate, measured in RPM (revolutions per minute) and spin efficiency measured as a percentage. Spin efficiency is defined as how consistent, or inconsistent, a ball spins along a certain axis.

Key Points To Remember:

• Total Spin = Measured RPM Along All 3 Axes Of Rotation (X,Y,Z)
• True Spin = Total Spin Minus The Measured Gyroscopic Spin
• Spin Efficiency = Relationship Between True Spin and Total Spin

Let’s take all that we have learned so far and apply it to pitch movement.  Generally speaking, most fastballs, changeups and curveballs have a desired spin efficiency as close to 100% as we can get.  This means that the ball is spinning consistently along the same axis of rotation which will yield the most consistent air flow around the ball to determine movement.  As the air flows around the baseball, it experiences a phenomenon known as the Magnus Effect.  As the ball spins in a certain direction, it creates areas of high pressure and low pressure that will impact ball flight.  Additionally, the baseball is going to fight the force of gravity as it tries to pull the ball towards the ground on its way to the catcher.  For fastballs, the back spun baseball will fight gravity with the low-pressure pocket above the ball and a high-pressure pocket below the ball trying to keep it aloft on its path to the glove.

For curveballs, the top spun nature of the pitch will create an inverted low-pressure pocket which will force the ball to “break” downward with the aid of gravity.  The more efficient a curveball is spun and the higher the rpm, the sharper the break tends to be.  Hopefully you now understand the basic principles of how spin affects ball movement. 

This is all well and good but why do some fastballs tail arm side and some curveballs “slurve”? This all has to do with how the ball is oriented coming out of the hand.  Not every pitcher throws from a straight over the top arm slot.  For pitchers throwing from a three-quarter arm slot, a fastball may be tilted on the x-axis (reference the image above for orientation) so that the low-pressure pocket is no longer directly above the ball but perhaps closer to the 1 or 2 o’clock position (think where the z-axis is pointing).  This shift in orientation helps us explain why balls move in certain directions.  The same principles can be applied to top spun pitches like curveballs but because of the direction of spin, a curveball is going to move glove side as the low-pressure pocket shifts from the 1 or 2 o’clock position to perhaps a 7 or 8 o’clock position.  Use the picture as reference for hand position at ball release.

Key Points To Remember:

• Most Fastballs, Curveballs and Changeups = As close to 100% spin efficiency as possible
• Back Spun Pitches Will Try To Create Lift
• Top Spun Pitches Will Create Drop
• Tilt Of The Ball Out Of The Hand Can Explain How Pitches Move

In the previous section we attempted to explain how creating efficient spin is important for fastballs, curveballs and some changeups.  But what about sliders?  The short answer is, it’s complicated.  But that is why we are here, so let’s try and dissect this as simply as possible.

In general, most sliders will have significantly more gyroscopic spin than transverse spin.  You may have heard the concept of picking up the dot on a slider. 

This dot is created by the gyroscopic spin on the ball turning the seams into a dot and can be located on different points of the ball as it is thrown.  The image to the right shows what this dot may look like. Hitters will often look for this dot in order to identify the pitch on its way to the plate to adjust their swings.

By adding a little bit of transverse spin, a slider will begin to take on various movement characteristics based on the axis of this additional spin.  If you were able to perfectly spin a ball, like a bullet, of your hand with 0% efficiency, there would be no horizontal movement to the pitch on the way to the plate however that pitch will begin to fall vertically as it is creating no lift. By adding as little as 15%-25% transverse spin, the pitch begins to create the appearance of a slider.  The axis by which you are adding this spin will begin to define the overall shape of the pitch, both vertically and now horizontally.

There are many different kinds of sliders that a pitcher can throw.  Some have a vertical break (Think Brad Lidge) and some create a more sweeping horizontal break (Think Adam Ottavino).

The different break characteristics can be attributed to different release points and different axes that the balls are spinning on. Lidge averaged 1.25” of horizontal break and 0.74” of vertical break on his slider over his career while Ottavino has so far averaged 5.98” of horizontal break and -0.12” of vertical break on his. On Lidge’s slider, we can make the assumption that his slider has less transverse spin which allows for him to create more vertical movement while on Ottavino’s slider we can make the assumption his slider carries more transverse spin which allows for a bigger sweeping action.

Ideal sliders are difficult to define because they come in so many different variations based on arm slot and spin. When developing a slider, it is fair to assess the pitch based not only on movement, but also on how it fits in with the rest of the athlete’s repertoire. Some athletes have a difficult time creating the right amount of transverse spin to create a big enough sweep to make it an effective pitch while other athletes will find themselves adding too much transverse spin and creating more a slurve which would be halfway between the vertical characteristics of a curveball and the horizontal characteristics of a slider.

Key Points To Remember:

• Most sliders will have more gyroscopic spin vs transverse spin
• Sliders come in all shapes and sizes and are difficult to define
• Ideal slider spin efficiency is somewhere between 15%-25%

Measuring spin with the aid of technology that costs thousands of dollars in definitely a luxury for most coaches, programs and facilities.  While they are becoming more popular within the world of baseball, they may be financially out of the wheelhouse for some.  So, can you still measure spin rate without the use of expensive technology?  The answer is yes but with some limitations.

Early on in our facility’s existence, we didn’t have the means to invest in Rapsodo so we went the low tech way.  Most everyone has a very capable cellphone in their pockets these days.  Most of these modern cellphones have a slo-mo feature shooting upwards of 240fps (frames per second). By simply drawing a thick black line on a baseball in various directions and a solid dot on the sides you can use your phone, and these marked up baseballs to see how consistent a ball is spinning in various directions.  For four seam fastballs, curveballs and changeups, simply draw a solid line around the ball across the four seams.  For two-seam fastballs draw a solid line around the ball going with the seams and across the sweat spot.  On both baseballs, draw solid circles in the horseshoes on either side of the stripe. Have your athlete throw these balls to a target and stand over their shoulder with your phone to capture the pitch in slow motion.  You will not get any measurements or numbers, but you can see how efficient the spin is by watching the line rotate around the ball or watch the dot spin in place.

Hopefully by reading through this blog, we have made it easier for you to understand the basics of spin and spin-rate.  There are definitely more advanced concepts when it comes to spin and how it effects ball flight but we want to try and keep it as simple as possible to understand.  Coaches should not be afraid of spin or just write it off as a useless technological measurement.  While the eyes do tell us quite a bit, having a little bit of advanced knowledge can be a difference maker between and average pitch and an elite pitch.