Pitches and Stuff: The Slider

Why does a curveball curve? How does a pitcher throw a changeup with the same arm speed as a fastball? Baseball is filled with buzzwords that are often used imprecisely. In this series of articles, Mike Richmond explores the baseball’s motion as it travels through the air: How does it behave, and what can a pitcher do to control it? This article looks at the slider to see what causes its very distinctive break.

What effect do different grips have on pitches? What’s the difference between a cutter and a slider? The art of pitching is filled with arcane terms, and even when two players are talking about the same thing, they often use different words. In this series of articles, we’re going to look carefully at the motion of a baseball through the air: how does it behave and what can a pitcher do to control it?

Today, we focus on the slider. Typically, a slider is a pitch which seems to fall between the common classes; not truly a fastball, nor a curveball. How does a slider behave, and how does a pitcher throw it? Although deep understanding of this pitch requires some vector calculus, don’t worry – we’ll use pictures to make the math easy.

What Makes a Slider Different from Other Pitches?

The most fundamental property of any pitch is its speed. In the graph below, the speed is shown on the vertical axis. Looking at pitches thrown by Zack Greinke of the Arizona Diamondbacks in a game against the Dodgers last year, we see that there are some leisurely ones (curveballs, denoted by pink symbols) and some electric ones (fastballs, marked by red and green symbols):

Two sets of pitches fall in the middle: the changeups, which appear as blue crosses on the left, and the sliders, which are shown as brown triangles on the right. It seems that sliders aren’t particularly fast, nor particularly slow.

Another property of pitches is their break. Most commonly, that is the difference between their trajectory and that of a ball thrown with the same initial velocity, but no spin. As you may recall from earlier articles in this series, a basic fastball breaks up, while a basic curveball breaks down. A pitcher’s arm angle can modify these motions, so that a righthanded pitcher’s (RHP’s) fastball moves tends to move toward third base, as well as up.

Looking at a slightly different graph we can observe how a slider breaks. As seen below, the y-axis shows vertical break, while the x-axis shows horizontal break (note that speed does not appear on this graphic). The brown triangles are sliders:

The typical slider is a peculiar cross between fastball and curveball: It breaks up, like a fastball, but moves horizontally towards first, like a curveball. Batters who guess curveball will swing below the slider, while hitters who are thinking fastball will instead see the ball glide away from the bat.

Sounds great! But how does the pitcher make the ball behave in this way?

How to Throw a Slider

Let’s begin by reviewing the mechanics of throwing a fastball. The goal of the pitcher is to eject the ball from the hand with the maximum velocity. To do so, he employs the longest, straightest launching system, running from the shoulder, through the arm, elbow, wrist and palm, all the way to the tips of the fingers. In the figure below, shown from the batter’s point of view, a right-hander is about to release a fastball:

Let’s focus in on the pitcher’s hand at the point of release. The gif below shows the ball rolling out between the index and middle fingers:


As the ball rolls off the fingers, its spin axis points towards third base, and slightly below the horizontal:

It is the direction of the spin axis that determines the break of the ball. A perfectly horizontal axis – corresponding to perfect backspin – would yield a fastball with perfect vertical rise. However, most pitchers tilt the axis slightly. For right-handed pitchers, the fastball breaks upward and toward third base. The opposite is true for left-handed pitchers: Their fastballs move up and toward first base.

Remember that a slider breaks up like a fastball, but horizontally toward first base, not third. That means the spin axis of a slider tilts the opposite way, pointing above the horizontal instead of below. How do pitchers hold the ball to make a slider “slide?”

The answer is that pitchers shift the location of the ball within their hand by one finger; instead of coming off the hand between the index and middle fingers, the slider rolls out between the index finger and the thumb:

Releasing the ball between index finger and thumb causes the spin axis to tilt the opposite way, slightly above the horizontal:

The difference in the grip is obvious in slow motion – but very hard to pick up at the plate, at game speed. Look at the ball nestled between Sean O’Sullivan‘s thumb and fingers in just before the gif starts:

The advantage of this technique is that it causes the ball to move in a new direction – one that might befuddle a batter. The drawback is that the lack of support from two long, strong fingers causes the slider to leave the hand moving more slowly than a fastball.

Using the Slider Wisely

So, the slider is a pitch which

  1. is fast for a breaking ball
  2. and breaks horizontally in the direction opposite to a fastball

How can a pitcher use the slider effectively?

One common situation arises when a pitcher faces a “same-handed batter” – a righty pitcher matched up against a right-handed batter, or a southpaw against a left-handed batter. In these matchups, a fastball breaks toward the batter, while sliders and curveballs break away from the batter. If the pitcher aims his slider toward the outer half of the plate, it tends to move farther and farther away from the batter as it approaches him – perhaps ending up far outside the strike zone.

Certain relief pitchers specialize in this type of slider. Known as “Lefty One Out GuYs” (LOOGYs) or “Righty One Out GuYs” (ROOGYs), they are brought into a game to face a dangerous same-handed batter. They usually feed the opponent a steady diet of these “runaway” sliders, tempting the batter to swing at a ball that looks like a strike – but isn’t.

In the video clip below taken from a game played on May 3, 2016, the Marlins’ Kyle Barraclough induces Yasmany Tomas to swing at a “runaway slider:”

This strategy won’t work against batters who are opposite-handed as the slider isn’t moving away from them, but instead breaking in towards them. In this situation, a pitcher may choose to throw a slider that initially appears to be missing the plate to the outside but, as it breaks back inside, just clips the outer edge for a strike:

When thrown properly, the backdoor slider is nearly impossible to hit. The batter’s first reaction is “that ball is way outside – let it go.” By the time he realizes that it may be a strike, it’s too late to swing.

Jose Fernandez of the Marlins executes this strategy perfectly, striking out Jason Heyward to end the eighth inning of a 9-0 win:

The slider is a staple for most major league starters. It is an effective pitch because it combines and blends aspect of the fastball and the curveball, effectively confusing the hitter when thrown with the proper spin, break, and velocity.

Follow us on Twitter @SoSHBaseball.
Featured image courtesy of Adam Hunger.
About Mike Richmond 12 Articles
Michael grew up on the South Shore of Massachusetts, but rebelled against his parents by rooting for the Orioles (eventually, he came to his senses). After receiving his Ph.D. in Astronomy from UC Berkeley, he spent five years as a post-doc at Princeton working on the Sloan Digital Sky Survey. He now lives in Rochester, NY, studying supernovae and listening to baseball games far too often.

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