This article was written by Greg Zumach and Steven Pappas, a Cubs fan, future statistics major, and truly one of the better analytical minds in Cubs fandom. He serves as an analytics guru for North Side Bound. You can and should follow him on his Twitter account. He also writes for Diamond Digest.

At North Side Bound we want to Make Sense of the Metrics to make baseball accessible to every fan. We understand that everyone enjoys the game for different reasons. Some love the simplicity of a game that, at its roots began as nothing more than “bat hits ball”, while others would tune in to every Statcast telecast possible so they can pair advanced metrics with the action on the field. We’ll be exploring a very specific pitch metric here in this article, but for those that don’t have (or want) a background in pitch development, we’ll still be breaking it down as we go along. There are a few sections that feature more advanced pitching metrics. Make sure to check out the following Primer for terms used in this article.

Vertical movement: The amount of movement (in inches) imparted on the vertical plane solely by the force of a ball’s spin. It’s also referred to as IVB, carry and ride. The average four-seam fastball has about 16 inches of vertical movement.

Horizontal movement: The amount of movement (in inches) imparted on the horizontal plane solely by the force of a ball’s spin. It’s also referred to as run. For instance, the average four-seam fastball has approximately 7.5 inches of horizontal movement.

Cut: Fastballs with “cut” have natural movement to a pitcher’s glove side, meaning that if a righthander threw a cut fastball the pitch would move away from a right-handed hitter or in towards a left-handed hitter.

Carry or Ride: A four-seam fastball with carry or ride gives the illusion it is moving upwards. An overhand delivery ensures that a pitch can’t defy physics and actually move upwards, but a fastball with nearly perfect backspin will drop less and make it appear it’s moving upwards in the zone. For the analytically inclined, these have high “IVB” -Induced Vertical Break.

Spin: The amount of revolutions (spins) per minute (RPM) the ball makes while being thrown. While higher spin RPM can be very helpful in pitch design, lower spin can also be advantageous. The amount of spin that translates to movement is referred to as spin efficiency or active spin. Spin efficiency is the percentage of spin (in RPM) that contributes to movement. Another term for this is active spin because it’s percentage of spin that actively affects pitch movement.

The Cubs are in the midst of a pitching revolution. After heavily incorporating sweeper sliders into pitching development infrastructure and showcasing pitchers who feature cut-ride fastballs, the Cubs are starting to garner national attention. Driveline’s own (and former Cincinnati Reds minor league pitching coordinator), Kyle Boddy, listed the Cubs among the leaders in xERA.

Seeing the Cubs ranked among the organizational leaders in any pitching category is an exciting development, but when it’s being featured by Boddy, it intrigues even more. So what is “xERA” and does it matter the Cubs are currently one of the favorable organizations in the metric in the MiLB? Most fans are familiar with ERA (earned run average), which calculates the number of earned runs (runs that aren’t due to errors or passed balls) a pitcher allows per nine innings. With ERA considered one of the oldest stats, teams, analysts, and fans have known for some time that it doesn’t quite describe pitching success. A next-generation statistic like xERA incorporates how much contact a pitcher gives up and the quality of that contact using Statcast data like exit velocity and launch angle. While it still doesn’t paint the whole picture, it’s somewhat like an artist moving from fingerpaints to watercolors, giving the audience a more accurate view. That quality of contact will be critical as we examine why the Cubs may be succeeding in this area. So how are the Cubs limiting hard contact? It might just be using a heavy diet of gyrospin fastballs.

What is Gyrospin?

Gyroscopic or gyro spin, otherwise known as football, bullet, and rifle spin, is spin that doesn’t contribute to movement. With perfect gyro spin, only external forces will act on the ball, notably gravity. In baseball, this type of spin is most common with cutters or sliders. Luis Castillo, for instance, throws a slider that has almost no spin-induced movement. GS pitches are categorized as “less efficient” because the amount of spin affecting movement is lower.

Authors note: if you’re head is spinning (pun intended) reading this, skip down to the table below.

When it comes to gyro fastballs, most are thrown with a healthy mix of backspin or side spin and gyro spin. It usually results in spin efficiencies greater than that of most cut fastballs, but less than most fastballs with backspin. Often, these pitches will have a noticeable seam-shifted wake effect. While seam-shifted wake would require article(s) focused solely on the topic, it’s when the seams of the ball affect the movement of the ball more than it would be expected to based on the other metrics.

In general, fastballs with higher efficiency (higher active spin and less gyrospin) have been more coveted in the game. Trying to help develop pitchers to throw a more efficient fastball is common in pitching development circles. The pitchers that throw more efficient fastballs tend to be those that throw the ball in a pronated position (palm more direct to the plate), and pitchers that throw with more gyrospin throw in a supinated position (palm more inward). You can see this visually in the following tweet from Driveline’s Chris Langin. The first clip (“less efficiency”) features more supination and the second clip is pronated. That supination comes into play later, but if that concept is still confusing, don’t worry. Let’s show you some numbers that get to the heart of why we should care about GS fastballs.

How do gyro pitches compare to those with more horizontal movement?

When comparing our classification of fastballs that have gyro and don’t, we found that gyro fastballs average considerably less run. The spin-induced horizontal break of a gyro fastball was about 1.8 inches, whereas non-gyro fastballs averaged about 7.6. Since most gyro fastballs also have some form of seam-shifted wake, horizontal movement would become more limited.

We utilized Baseball Savant data to group pitch types by their batted ball data. Here’s where things get very interesting. To get a gauge of a fastball with gyrospin without pitch-by-pitch spin efficiency, we separated four-seam fastballs by their horizontal movement. For instance, if a righty threw a fastball that had the expected run of a lefty’s, that’d be a gyro fastball. From this data, we observed a few notable trends.

Changeup (CH)86.37.2943964.724.
Curveball (CU)87.112.149476.9624.525.732.83.9
Cutter (FC)87.913.4509586.124.525.731.24
Fastball (FF)91.318.92100510.28.124.331.523.52.2
Gyro Fastball (FF)86.311.411045.84.125.825.833.64.7
Splitter (FS)86.73.510684.24.124.417.1454.5
Knuckle Curve (KC)87.95.812036.26.424.
Sinker (SI)89.55.2128376.75.224.716.941.84
Slider (SL)86.914.7141687.15.724.128.929.84.1

Gyrospin fastballs resulted in:

  1. The lowest average exit velocity of all pitch types
  2. Less barreled balls than regular four-seam fastballs, curveballs, cutters, sinkers, changeups, and sliders. Only splitters resulted in fewer barrels.
  3. The most “weak contact” out of all pitch types.

How many GS Fastballs do the Cubs throw?

A lot. Seriously, they aren’t messing around. The Cubs are the frontrunners in this classification of gyro fastballs, with about 14.9 percent of their four-seam fastballs having this kind of spin this season. They rank just ahead of the Royals, Orioles, Brewers and Dodgers. A primary reason for this is the emergence of Justin Steele’s fastball. Not only does he use the pitch over 50 percent of the time, about 71.4 percent of these four-seam fastballs have this variant of gyrospin.

Which Cubs MiLB pitchers throw GS fastballs?

This is a Cubs minor league blog, right? Yes, you’re correct. Unlike Savant data, minor league pitch-tracking and batted ball data isn’t so readily available. Both Steven and I would like to thank the the individuals that were willing to share bits of information so we could create this piece. There are a few notable pitchers who throw fastballs with GS or GS-like (Cut-ride) movement.

Ben Leeper

An undrafted free agent from Oklahoma State in 2020, Leeper’s gained prominence due to his fastball-slider mix. His four-seam fastball doesn’t quite have the gyrospin of someone like Steele, but they still share some similarities. Leeper throws his fastball with backspin, meaning a majority of his spin is converted to movement. However, his spin direction is primarily vertical, meaning that he still gets the little run reminiscent of gyro fastballs. One of the most prominent pitchers with this profile is Dylan Cease. Leeper likely has the same spin direction as Cease, but his fastball has less spin, vertical movement and velocity. Despite this, it still grades above average in all three of those metrics.

MLB Comparables – Chase De Jong (PIT), Bryan Baker (BAL), Drew Rasmussen (TBR), Wil Crowe (PIT)

Ben Leeper’s fastball

Porter Hodge

Hodge, the Cubs’ 13th round pick in 2019, has broke onto the scene with the Myrtle Beach Pelicans this season with his fastball-heavy mix. Similarly to Steele, Hodge cuts the pitch significantly, meaning it has prominent gyro fastball characteristics. He similarly spins the ball well at a low velocity as well. A unique factor of his, however, is that he has a lower release point than league average with significant extension, measured at over seven feet. It’s not quite to the extent of an Edwin Diaz or Trevor Williams, but it may still aid him nonetheless.

MLB Comparables – Zach Thompson (PIT), Blake Taylor (HOU), Carl Edwards Jr. (WSH), Justin Steele (CHC), Brad Keller (KCR)

Porter Hodge fastballs “it has a bit of cut to it”

Exploring next steps

For years assessment of the Cubs pitching prospects was “they don’t have any.” Not only is this no longer the case, but there’s a compelling point to be made that the Cubs are among the leaders in various pitching development categories. One absolutely intriguing aspect of targeting pitchers with these fastballs is that since most of these pitchers are natural supinators, it’s easier for those pitchers to learn and perfect sweeper sliders. Steven and I aren’t done exploring pitch design, but we hope this stirs some conversation.