Why Are Sliders So Hard to Hit?

Patrick Corbin had one of the best sliders in baseball in 2018. (via Not That Bob James)

If you were to line up all the pitchers in baseball by the number of pitches they threw in 2018, starting with those who threw the most and ending with those who threw the least, you’d learn something about the various strata of major league pitchers, but it’s something you likely already knew.

It starts with the aces, the workhorses, the perennial Cy Young contenders. At some point after Blake Snell, you start getting to the “good but often hurt” pitchers, mixed in with the “always healthy but are they good?” That layer goes on for a while, eventually hitting Homer Bailey and the rest of the “Wow, we need five starters? Are you sure?” pitchers. The starter list ends with elite relievers, before transitioning to mop-up men, then role-specific relievers, and then the odds and ends who always populate the back end of baseball leader boards and Wednesday night trivia questions.

It’s a relaxing exercise because it convinces you that you understand baseball, or at least pitching, and the sorts of people the occupation molds.

But while the types of pitchers are simple and stratified, the effectiveness of their pitching can bamboozle. Take for instance this list of nine pitchers: Patrick Corbin, Edwin Diaz, Seranthony Dominguez, Jace Fry, Ryan Pressley, Tanner Scott, Will Smith, Pedro Strop, and Blake Treinen. They all have one thing in common, but could you guess what it is?

They aren’t the same type of pitcher — there’s an elite starter, a handful of elite relievers and three guys named Smith, Scott and Fry. Not all of them were successful nor were they all consistent. No, what these nine pitchers have in common is that they possess 2018’s nine most unhittable pitches based on whiff percentage, and every single one of those pitches was a slider.

If you read Jeff Sullivan’s FanGraphs piece on Ryan Pressley in early October, neither that list nor Pressly’s presence on it should be surprising. Pressley’s slider generated a 31.9 percent whiff rate across the regular season and October, meaning one in every three sliders Pressley threw resulted in the batter swinging and finding nothing but air.

While Sullivan went deep on what makes Pressley’ particular pitch so troublesome for batters, it was the rest of the top 10 that caught my eye. All were sliders, save Hector Neris’ splitter at number nine.

I updated the rankings to include pitches thrown through the 2018 postseason, keeping the 250 minimum pitch cutoff. Blake Treinen bumped up to eight, and Dominguez and Neris each moved down a spot. If you expand the leader board further, 21 of the top 30 and 28 of the top 50 most unhittable pitches in baseball are sliders.

Across baseball, the slider is only the second most unhittable pitch, registering an average whiff rate of 17.5 behind the splitter’s 19.4. The splitter benefits from its relative scarcity, though, as only 16 pitchers threw qualifying splitters. Meanwhile, sliders were the second most thrown pitch in the majors. Batters can expect to see a slider in every single game they play, yet still it confounds.

Average Whiff Rate by Pitch Type
Pitch Type Whiff Rate
Fastball 9.66
Cutter 12.88
Change 16.74
Curve 13.64
Slider 17.52
Spliter 19.41
Sinker 6.60

Why then, with so much familiarity, are sliders so hard to hit?

Dr. Donald Teig has worked with 15 major league teams over his career as a sports vision consultant, translating his optometrist background into something teams and hitters can use to excel at the plate. Yet, his main piece of advice can be heard on any Little League field on any given summer Saturday: Keep your eye on the ball.

Granted, he also admits it’s not as simple as that, and that hitting a baseball may be the hardest thing to do in professional sports. He teaches hitters to soft focus their eyes on a pitcher’s cap or somewhere near his release point, and then, right when a pitcher releases the ball, hard focus on the pitcher’s hand. To facilitate that hard focus through the pitch, he tells his players to look for the letter “R” in Rawlings.

“Let’s face it — nobody sees that ‘R’,” Teig said. “But the effort you make to do that forces you to keep your eye on the ball.”

While soft focus to hard focus simplifies how players can keep their eye on the ball, most of the work of hitting actually has to do with genetics. According to Dr. Daniel Laby, an ophthalmologist specializing in sports vision who currently works with eight major league teams, major league players have 20/12 eyesight on average, meaning they can see two lines further on an eye chart than your standard 20/20 vision human.

If a player comes in with 20/20 eyesight thinking he has perfect vision, Laby will give him corrective lenses because the standard human vision just won’t cut it.

Beyond vision sharpness, Laby stresses that players also need to see contrast in short-viewing times. The player needs to distinguish red seams on a white ball in about 400 milliseconds from hand to plate — far different from reading letters on a stationary paper.

“We have a test where we show targets that are small, faint and we show them for 100 milliseconds,” Laby said. “And that’s how we test to make sure the batter has the visual ability necessary to do this — identify the spin and the dot on the ball.”

Laby’s test shortens the time allowed to 100 milliseconds because even though it takes a pitch around 400 milliseconds to reach the plate, a player’s visual system can no longer physically track a pitch after the first 200. For context, 400 milliseconds equals the time it takes to blink. Players have half a blink to track a ball, read the pitch and decide to swing.

“Most of these batters are thinking to swing and then they inhibit the swing,” Laby said. “In other words, they almost want to swing at every pitch and then they decide in the first 150 milliseconds that they don’t want to swing and they stop it.”

It sounds like an impossible enterprise for any pitch, much less one that moves like a slider. But players have their tricks. Change-ups come out of the hand slowly, according to Kansas City Royals outfielder Brett Phillips. Curveballs jump up a bit out of the hand. Some pitches knuckle and sometimes you can see different finger grips before release. But sliders?

“If you’re tipping a pitcher, that’s the only way you’re going to know that it’s a slider,” Phillips said.

A pitcher uses a similar grip for a slider as he would for a fastball, slightly turning his hand on release and letting the seams create a sliding movement that begins about halfway to the plate. After the batter’s visual system has given up in other words.

Further confounding the hitter is the slider’s unconventional movement, with horizontal as opposed to vertical break.

“In baseball, being that every pitch thrown is vertical and you learn to play the game hitting vertical movement of the ball, the slider is a freak compared to all the others,” Teig said.

Because actually hitting a baseball is dependent on instinct and muscle memory developed through endless repetition, encountering a pitch with movement that contradicts that muscle memory adds another layer of difficulty to hitting. Teig adds that even though the logical jump of the ball moving laterally with the plane of the bat may incidentally help a hitter, it often doesn’t make a difference because the surprise of a ball moving contrary to expectation still overrides a batter’s muscle memory, or visual-neuro-cognitive memory as he calls it.

Outside of the science of our eyes, so much of what makes a slider hard to hit, according to Phillips, derives from the increasing velocity of the average fastball. For a pitcher like Jordan Hicks, whose average fastball sits at 101 mph, a slider can be a devastating complementary pitch. The fastball has already cut down the time to plate from 400 milliseconds to 350 or less, so a batter has to react even more quickly to catch up to it with less room for adjustment to a slider.

“With a guy throwing 102 mph, you still have to be on the fastball and obviously if he throws you a slider you have to get lucky,” Phillips said. “And I hate to say it but that’s how hard it has gotten to hit off those guys who are throwing a 100 mph and then they throw a 92 mph slider at you.”

To prove Phillips’ point, in 2018 pitchers with slider whiff rates over 25 percent had an average fastball 2.8 mph faster than pitchers with slider whiff rates below 13 percent.

Velocity doesn’t tell the whole story, though; otherwise Hicks’ 20.5 slider whiff percentage would be about 10 percentage points higher. In fact in 2018, fastball velocity accounts for only 17 percent of the variance when modelling slider whiff percentage. A pitcher needs to control his slider in tandem with his fastball, otherwise it becomes a waste pitch.

Phillips says the best slider he’s faced is Max Scherzer’s because the Nationals’ ace can spot the pitch where he wants, whether he’s going for a backdoor looking strikeout or a back foot swinging one. Scherzer’s slider was thrown for a strike 47.9 percent of the time in 2018, the highest percentage of any pitch in his repertoire, and its 27.5 whiff percentage made it the 12th most unhittable pitch in baseball.

Scherzer may have thrown the nastiest slider of all 2018 back in July, when he got Sandy Leon to strike out on an offering that nutmegged the Boston catcher.


In his piece on Pressly, Sullivan pointed out the part of the jump in Pressly’s slider effectiveness, from 15 percent whiff rate in 2017 to 32 in 2018, could be attributed to him placing in in the bottom right of the zone, instead of down the pipe. The rest of the sliders in the top 10 also showed bottom edge of the zone placement, even though pitchers’ average fastballs ranged from 91.4 to 98.6 mph.

Which leads us to tunneling, the final key to why sliders are so difficult. If a pitcher is throwing near a 100 mph before dropping a slider, a batter could hypothetically bank on recognizing that the ball is traveling a different path — either outside to come in or inside to go out — than the pitcher’s fastball.

But the best pitchers emphasize tunnelling their pitches, or keeping a breaking ball in the same path as a fastball for as long as possible before the break.

Here’s Max Scherzer again, with his fastball and slider overlaid:


Right until that 200 millisecond point of no return, the pitches look exactly the same. Jose Altuve swings wildly at a shoulder-high fastball while watching the slider paint the bottom of the strike zone. Scherzer effectively eliminates any information Altuve’s visual system could use to distinguish between the pitches, minus one tiny, nearly imperceptible cue.

When a slider spins, the seams create a small red dot for which some hitters look. It’s one miniscule visual clue sliders give away, but it turns out that clue is almost entirely useless.

Both Laby and Teig said that even if a hitter is looking for a red dot, he likely wouldn’t have time to adjust to the slider with the remaining 200 milliseconds. Phillips added that when a pitcher is throwing as hard as Scherzer, you don’t even try to look for the dot. There’s just not enough time.

And trends show that it’s only going to get harder and harder for hitters. Since PITCHf/x was introduced in 2007, the average fastball velocity has increased 1.5 mph. The prevalence of extraordinary heaters has nearly tripled as well. In 2018, 198 pitchers’ fastballs averaged at least 95 mph compared to only 68 such pitches in 2007. A hitter can expect at least one flamethrower every game now, and more likely than not, a parade of them.

So why are sliders so hard to hit? Because even the most advanced visual systems among us have trouble differentiating them from fastballs. And that visual system cannot physically track the path of the ball by the time it begins to break.

The next time you see a poor batter get nutmegged by a Max Scherzer slider and feel the urge to yell, “How can you swing at a pitch between your legs!” remember: that batter likely has vision far superior to yours and has spent years training his body to hit a 100 mph object, which is what he thought that ball between his legs was going to be until the half blink before it moved.

The real surprise is not that the nine most unhittable pitches of 2018 were sliders, but that someone managed to hit a slider at all.

References and Resources

  • Jeff Long, Baseball Prospectus, “Pitching Backward: An Ode to the Slider
  • Interview with Dr. Donald Teig, conducted October 29, 2018
  • Interview with Dr. Daniel Laby, conducted November 1, 2018
  • Interview with Brett Phillips, conducted November 4, 2018

Wes Jenkins is a staff writer at Redleg Nation and freelances when he can. You can follow him on Twitter @_wesjenks or check out more of his writing on his website, wesjenks.com.
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5 years ago

I’d love to know what percentage of players with 20/20 vision wear contacts.

Jetsy Extrano
5 years ago

This is good stuff, but I think you can’t talk about why sliders are hard to hit without talking about handedness. Because it’s same-handed sliders that are hard to hit.

Sliders “slide” across the zone mostly not because of spin deflection — it’s great to have, but some good sliders are near zero — but because of the geometry of relative handedness. Just letting that play without same-handed fastball spin straightening the path to the eye.

5 years ago

Great article.

5 years ago

Great Article! Ted Williams and his 20/10 vision even admitted that the Slider was the pitch he struggled with the most…