Adding Slider Depth

Ethan Moore
Apr 21 · 5 min read

As I’ve hopefully established by now, I am very interested in pitch design and its potential benefits for a player and therefore for a team. Today I went looking for potential signs of offseason pitch design in the MLB by looking at pitchers whose movement on one of their pitch types has changed the most from last year to this year.

By watching some Driveline Plus videos, I’ve been learning more about why the slider moves the way it does, and why slider movement can vary widely from pitcher to pitcher. So, naturally, I was excited to check out the pitchers with the largest gap in their sliders’ vertical movement from 2018 to 2019. In common terms, which pitchers are getting more depth on their sliders this year?

After some FanGraphs Leaderboarding and R manipulating, I arrived at this list:

Marlins reliever Adam Conley may not be the most exciting name I could have hoped for on this list, but that margin is pretty noteworthy. Something to make a young analyst feel alive for a second. Conley has gained two more inches of drop this season than anyone else!

(Note: I read a book, I think it was How Not to be Wrong: The Power of Mathematical Thinking, that talked about why the towns with the highest and lowest rates of heart disease were almost always some small rural town because there are lots of these small towns, and the small number of people means there will be lots of variance. It’s easier for Nowhere, Kansas to have 40% of its deaths happen by heart disease than it is for Chicago to put up such a number. This is the danger of small sample sizes.

Adam Conley, according to Baseball Savant, has only thrown , so we may be encountering a “small town” with an extreme statistic here. But because the characteristics like movement and velocity don’t have many outside forces or randomness acting on them, they “stabilize” pretty quick, so 34 pitches, and with such an obvious change in the pitch’s movement, I’m gonna go ahead and say that what we’re seeing here is real.)

What does a difference of almost 6 inches of downward break look like? Let’s take a look thanks to Baseball Savant:

Conley’s 2018 Slider:

+3.7 inches of vertical movement

Conley’s 2019 Slider:

-2.1 inches of vertical movement

Now let’s check out The Numbers (TM):



If you’re not familiar with a pitch movement chart, what I want you to notice is the yellow circle, representing the slider, and how much lower it is in 2019 than in 2018. That’s what 6 additional inches of depth looks like on paper. (Also note the 6 mph decrease in velocity on the slider, which I’ll talk about later.)

This certainly looks like the result of a concentrated effort to change the shape of the pitch, hopefully to be more effective (we’ll have to wait for a larger sample to make any conclusions about that, but the graphs above show that he is throwing his slider about 50% more often than he did last year, so something must be working). That’s cool! But how did he do it?

One of the most basic and necessary things to know about pitch movement is that topspin causes pitches to go with gravity, making them drop, while backspin causes pitches to defy gravity for longer, giving them “positive” vertical movement and the appearance of “rising” through the zone. You can remember this because curveballs always have topspin so they always drop, and fastballs always have backspin so they always have positive vertical movement. But the fun thing about sliders is that they can have either topspin, backspin, or neither (called gyro-spin where the ball spins like a bullet).

So last season, Conley’s slider had almost 4 inches of positive vertical movement, and we can see that in the gif above. The pitch, at first glance, appears to be more like a cut fastball than a slider. We could qualm about whether it actually was a cutter or a slider, but we’re just gonna go with MLB’s pitch classification model alrighty? Let’s take a look at what a slider thrown with backspin looks like up close:

Notice how he throws through the ball and not around it? This pitch has worked well for deGrom, but knowing that it has backspin helps us understand 1) why it’s so fast, and 2) why it doesn’t drop very much. This is kind of what Conley’s slider spin looked like in 2018.

For some much needed context, let’s check out a slider thrown with backspin:

See how he appears to pull down on the side of the ball to create some topspin here? That’s why Kluber’s slider drops so much more than deGrom’s (and is slower, as it’s much easier to throw a fast pitch with backspin than a fast pitch with backspin.)

Although I couldn’t find any up-close footage of Adam Conley’s sliders at release (he’s a little off Pitching Ninja’s radar I guess!), I’m very confident that this change, from a backspinning slider to a topspinning slider, is how Conley achieved such an increase in depth on that pitch. Also, the fact that the new slider lost 6 mph provides further proof that it’s now being thrown with backspin.

I have little practical pitch design experience, so I can’t attest to how easy or hard that process would have been for Conley, or for any pitcher, but I will say that the process may be simpler than many might assume from the outside. Our collective understanding of how and why pitches move the way they do, and what we can do about it, is growing quickly, and it’s exciting to see the results of the pitch design and development process on the field affecting the game in a tangible way.


In this great during Spring Training 2019, he details how he changed his mechanics to better get around the breaking ball and how he added more than 5 miles per hour to his fastball. Here’s a guy who’s dedicated to his development and I have no doubt that the changed slider is a part of all this.

Something Tangible

Ethan Moore's musings on the aspects of baseball analytics that are of personal interest to him

Ethan Moore

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Cal Poly Baseball Analytics

Something Tangible

Ethan Moore's musings on the aspects of baseball analytics that are of personal interest to him