The Slider Moves Differently to Different Locations

I gave Royals’ right-hander Chris Young a bit of an incredulous look — “You’re throwing the slider a ton this year!” He shrugged. Sure. “It’s okay, you can throw it inside and out, and it’s been good. But it moves a little differently depending on where you throw it.”

Young then mimicked the release point when trying to throw a slider inside to a right-handed hitter, and then he showed where the release point might be when throwing it outside to a right-handed hitter. One was straight to the plate, and the other had more side-to-side finish to it.

If you’ve pitched competitively — or, at least, possess more experience than my own, which is limited to throwing a whiffle ball to my kid while he imitates Julio Franco — this may be old hat to you. But to me, it was surprising and also totally logical at the same time. I immediately wanted to know what this looked like.

Here are two ways of looking at it. In the first, I have plotted the movement of all the sliders thrown to right-handed batters by the top-10 right-handed slider-using starters last year. The movement is on the axis, and the color shows if the pitch was inside to righties (blue) or outside (orange). The second dashboard has split the inside sliders (px < -.4) from the outside sliders (px > .4) and colored the dots by velocity.

It’s not always easy to read these sorts of things, but generally the inside sliders are more vertical and tight, and the outside sliders are more horizontal. That jibes with what Young said. We can also see it here in tabular format, thanks to Matt Dennewitz’s K-means cluster analysis on the inside and outside scatter plots. That helps us find a two-dimensional average (the center of the clusters) that’s superior to averaging our values.

Sliders Inside vs Sliders Outside

Pitch	Horizontal	Vertical	Velocity
Slider Inside	1.6	0.7	85.3
Slider Outside	2.7	1.6	86.0

Inside = inside third of plate or px < -.4
Outside = outside third of plate or px > .4

That’s 824 sliders on the inside third and 3229 sliders to the outside third — and the sliders to the inside part of the plate have an inch-plus less horizontal break and an inch more vertical break. Pitches to the outside are also almost a tick faster.

That may not seem like much, and it won’t show very well in a GIF where a six-inch difference yesterday didn’t wow the crowd, but it’s supported by most of the pitchers to whom I spoke.

Here’s Jeff Samardzija on the topic, for example: “A little more depth glove side than if you throw inside, because you can’t get around the ball. You’re just throwing it to get a little movement and change the speed. On the outside corner, you can grip on the ball and not only is the spin making the ball move, but your arm is making the ball move. Inside? Less depth, it’s a smaller move. If it goes over the plate, it gets tatooed. But if you can execute it, they won’t swing at it, and it’s a good pitch because it’s a ball out of your hand. Risk/reward pitch for sure.”

And Zack Greinke: “It’s more down on the inside and more sweeping and big on the outside corner, yeah.”

And Madison Bumgarner: “I don’t feel like it’s very much different, I just throw the same one. But you have to get a feel for it. Sometimes you’ll see guys step a little further towards the outside part of the plate when they’re throwing there. So then it’s really the same as throwing inside.”

There are a few interesting things going on here.

For one, the movement matches what you might want from an outside slider. You’d probably rather have it continue on out of the zone, rather than stay inside the zone and remain hittable. And on the inside, there’s no way you’d want it to leak horizontally over the middle of the plate. So you throw a little baby up-down slider that should stay inside.

The second is that, if you’d rather have the more vertical version, you can alter your mechanics slightly in order to get that version on the outside corner. That means that, in reality, this effect might be larger. Some pitchers are presumably doing this now and softening the effect we see in the results.

A pitcher is, in effect, changing his arm slot if/when he changes his release point. It follows, then, that he’s changing the spin axis on the ball, as well. Samardzija sort of talks about this when he mentions spin and arms. When you release further out in front, you’re taking more advantage of the sideways spin — with a more sideways release point, in other words — and so the ball goes more sideways.

Does this have implications for the viability of fastball/slider starters? An inch here or there is not a great way to live, for one. When I talked to Greinke about a pitcher with many different breaking balls, his question was simple: “Are they all good?” Are these sliders really so different that they could function very differently?

And as much as a more horizontal slider might be effective in on the hands of a lefty, it still has more drop than a cutter, and still threatens to fall into that low and inside “happy zone” for a lefty slugger. That more sideways “outside corner” slider has four more inches drop than your average cutter, and that’s a bigger difference than the inside/outside sliders.

In any case, it’s a thing to watch for. It’s a thing with which pitchers are dealing. It’s a thing that matters maybe just a little bit. Pitches seem to move differently when thrown to different locations. The more you know!