On one of his first pitch design days this winter at Driveline Baseball’s facility in Kent, Washington, Luke Jackson pulled out his phone and searched for a video of his ideal slider. “I know this is where this pitch should live,” Bill Hezel, Driveline’s manager of mechanical analysis, remembers Jackson telling him. “This is when I feel like it’s at its absolute best, I can throw it hard, I can command it, but I lose it sometimes…I just want it to go down.”

The video he was looking for was this one: an 87-mph pitch disappearing below Bryce Harper’s bat for strike three.

Luke Jackson gyroscopic slider, 2018 (credit: MLB)

Some sliders have horizontal movement, breaking right to left across the zone out of a right-handed pitcher’s hand. Other sliders, like Jackson’s pitch to Harper, produce exceptional vertical movement with little side-to-side bend. This is due to gyroscopic spin — think bullet spin or a football spiral — achieved by spinning the ball out of a right-handed pitcher’s hand like a clock as it travels towards home plate.

If it wasn’t for gravity, the pitch would travel on a straight line into the catcher’s glove. But the effect of gravity causes the pitch to “fall off the table” or break downward. While it might look like a curveball to the average viewer, the pitch rotates laterally as opposed to end-over-end towards the hitter. The pitch to Harper that Jackson showed to Hezel was exactly that: a vertical-breaking, gyroscopic slider. He just didn’t know it at the time.

Jackson first learned this slider early in 2018 from his Triple-A pitching coach while fiddling with his “spiked” curveball grip early in 2018. Months later, he arrived at Driveline, looking to understand and develop the pitch to its full potential. “I really wanted to see why [my slider] is good,” Jackson says. Adopting the pitch inflated his strikeout rate to 42% at Triple-A in 2018, but at times it became inconsistent. Jackson’s subsequent development of the pitch showcases the new age of pitch development and how technology has accelerated learning beyond reliance on thoughts and feelings.

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The Texas Rangers drafted the 18-year-old Jackson in the 2010 MLB June Amateur Draft from Calvary Christian High School in Fort Lauderdale, Florida. He spent the next six seasons bouncing between the majors and the upper levels of the Rangers farm system, even spending the first half of the 2015 offseason with Leones del Escogido of the Dominican Winter League. After the 2016 season, the Rangers traded Jackson to the Braves for former prospect Tyrell Jenkins and lefty Brady Feigl.

It was during Jackson’s stints with the Triple-A Gwinnett Braves in 2017 that he began working with Reid Cornelius, the club’s new pitching coach. Cornelius threw 211 major league innings for four teams and had spent the prior seven seasons as the Marlins bullpen coach. He had recently returned to the Marlins High-A team in Jupiter, Florida, after two seasons with the Braves.

The Braves outrighted Jackson to Triple-A twice in the first two months of 2018. That’s when he and Cornelius had a conversation about his spiked curveball grip. As Luke remembers, Cornelius simply looked at him and said, “Why don’t you just turn your hand over and throw it like a fastball?” Jackson listened and turned his spike curveball grip over into a standard fastball position with his index finger up. He threw 20 of them that day, each diving into the ground well short of the plate.

“Nice, those have good shape,” Cornelius told Jackson.

“Yeah, good shape, yeah,” Jackson responded, in a tone that suggested he had no idea what Cornelius was talking about.

“Now try to keep working it until it gets in the strike zone,” Cornelius said.

A Hardball Times Update by Rachael McDaniel Goodbye for now.

Luke Jackson’s spiked slider grip (credit: Lance Brozdowski)

Jackson tinkered with his new spiked slider for a week to no avail. “This is blasphemy,” Jackson remembers thinking. “He’s joking with me right now cause there’s no way that this works.” Even after multiple bullpens during which he struggled to find his command with the pitch, Cornelius still wanted him to use it in a game. So when he pushed a hitter to two strikes in a game not long after, his catcher put down a slider sign one more time after Jackson shook off the initial ask. “I was like, whatever,” Jackson recalls. The pitch bounced on the plate but fooled the hitter enough to earn a swinging strike three.

Despite his disbelief, Jackson had found a new weapon. “For about two weeks straight, I just started throwing it for fun with two strikes. and everybody swung at it. I was like, ‘This is wild,’” Jackson says. He brought his spiked slider up to the major leagues when the Braves recalled him on June 5, 2018, and started to rely on it more than he had in the past.

The seasoned vet Cornelius admits this is not the first example of a case of success for the spiked slider grip. He remembers showing the pitch to a Marlins Class A pitcher, Carlos Martinez, in 2004 with the Greensboro Grasshoppers of the South Atlantic League. While Martinez went on to throw only 15 1/3 major league innings with the Marlins, he developed a nice downward slider with the same spiked grip. “I’ve just seen some guys over the years throw it like that, and you can get on top of it better,” Cornelius says.

Current Cleveland closer Brad Hand started tinkering with a slider during his 2015 season in the Marlins bullpen. Cornelius mentioned the spiked slider grip, and Hand developed the pitch over time by playing catch. Hand’s slider usage jumped from eight percent to 30% the following season, and he now throws the pitch over 50% of the time. While he did not retain the spiked grip — his current slider grip is the same grip as his fastball — Hand’s initial tinkering with the pitch came under the tutelage of Cornelius. “It’s a tool that we use for them to get a feel for the slider coming off the middle finger,” Cornelius says. “You have to put pressure there, and you have to work through the ball to get some power to it.”

With his new spiked slider grip, Jackson’s strikeout rate jumped from 15% in 2017 at the major league level to 25% in 2018. He had started missing more bats, but his results lagged behind. While the increase in strikeouts drove his FIP down below 4.00 for the first time in his major league career, he struggled to prevent runs, posting an ERA above 4.00 for the fourth consecutive season. A component of this struggle came from the pitch’s inconsistency. That brought him to Driveline and Bill Hezel.

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Part of Driveline’s initial full assessment of a player like Jackson is determining his baseline pitch metrics. To do this, Jackson threw an abbreviated bullpen with a variety of tech running — Rapsodo, Trackman, and PITCHf/x. Driveline cross-referenced this info with publicly available information on BrooksBaseball and Trackman data from the Braves to show the movement profile and spin metrics of his repertoire.

Jackson’s first true pitch design session took place in the days after his baseline assessment. Driveline captured high-frame-rate (1,000-1,200 fps) footage with edgertronic cameras of each pitch Jackson throws — fastball, curveball, and slider. This created a catalog for Jackson to build on and access in the event he loses feel for the pitch during the middle of the season. “Say halfway through the year, [Jackson’s] slider starts…trending towards that cement mixer, bad cutter thing,” Hezel says. “He can go back and look at the edgertronic footage and give himself a refresher…This is the grip, this is what the ball is doing as it’s coming out of my hand, this is the wrist position, this is exactly what’s happening when this pitch is really good.”

As pitch design sessions advanced forward, Driveline started to communicate how they thought Jackson’s optimal slider should move and how to achieve sliders consistently in the desired window of movement. This broaches a feel-versus-reality complex. Ask a pitcher who throws a 12-6 curveball what he thinks his wrist and hand positions are and what happens when he throws it, and the reality can vary: “They’ll be like, ‘Oh, I’m pulling down, I’m getting really on top of the ball,’” Hezel says. “Usually they’re pretty under the baseball or on the side, and all the things they think are happening are not happening.” Driveline’s setup allows for immediate feedback and visualization of a pitcher’s release, giving them an understanding of how minuscule hand movements can affect the result of a pitch.

Luke Jackson’s spiked slider release, bullet spin (credit: Driveline Baseball, Luke Jackson)

Jackson’s spiked slider grip helps the ball slip off the inside of his middle finger and generate the desired bullet spin. “Seeing it — what made it good, what made it bad — helped me shape it,” Jackson says. His inconsistency came from how sensitive the spin axis can be on a slider. “He had a tendency to really think about trying to move the ball, over-exaggerating pulling the side of the ball,” Hezel explains. This can shift the nose of the ball left or right and alter the spin of the pitch. By pulling the side as opposed to letting it slip, an element of backspin is introduced. This counteracts the force of gravity pushing the ball down and can introduce a horizontal component.

For pitchers trying to throw a horizontal slider, this is ideal, but for Jackson’s vertical slider, this pushed it out of the desired movement profile. “That’s when [Jackson] gets into the danger zone,” Hezel says. “[His slider] ends up trending towards this bad cutter thing. It’s not cutting enough, it’ll back up and float.”

Below is an example of a slider Jackson “pulled” rather than let slip in 2018.

Luke Jackson “cement mixer” slider, 2018 (credit: MLB)

Jackson began to realize the pulling of his slider came from instances when he let his head beat him in his delivery, causing his arm to lag behind. He would get on the side of the ball, preventing the pitch from slipping off his middle finger. “It was mainly along the lines of finding what was the right depth to get it out,” Jackson says. “Get my finger on top of the ball, get it out in front of my head, make sure I see the depth.”

Gyroscopic sliders are a good fit for a pitcher like Jackson because they work around the inability to naturally spin a baseball over 2,800 rpm. (The average slider in 2019 has around 2,400 rpm; Jackson’s has around 2,500 rpm.) And spinning a baseball is something pitchers can’t easily tinker with unless using a foreign substance. “We don’t know what totally creates spin,” Hezel says.

If a pitcher throws a more horizontal slider, a high spin rate can help the pitch move, leading to a greater chance of producing swing-and-miss. Average-spin pitchers like Jackson, then, need to get creative. “The gyroscopic slider is basically just a shortcut to kill lift and get movement because you’re having a hard time creating movement yourself,” Hezel says.

While his spin might be average, Jackson’s slider is distinct beyond his grip. He possesses an innate ability to shift the nose of the ball downward with his index finger on ball release and retain the necessary bullet spin. “It’s not something I have seen a ton in our facility,” Hezel says. What normally happens when a pitcher shifts the ball nose down is coincidental movement left or right, which creates a pulling effect that engages horizontal movement, as mentioned above.

Jackson corrected his pulling but still holds this unique feature constant, whether consciously or subconsciously. He also throws the pitch hard, sitting inside the 85th percentile in the majors in slider velocity among pitchers with 50 sliders thrown. It also possesses nearly 9.5 inches more drop (98th percentile) than the average pitcher’s slider in this window of velocity. The result is a pitch with exceptional swing-and-miss numbers. His goal moving forward is to maintain the pitch’s effectiveness.

Sliders with more horizontal movement generally tend to be slower pitches than those with a more vertical component, like Jackson’s slider. One of the ways Jackson can use shorthand to tell whether his slider is in the desired movement bandwidth is to monitor the pitch’s velocity. “If he starts seeing his pitch trip more to 84-85 mph, that lets [him] know that pitch is not in that optimal bandwidth and we’re probably getting a little more horizontal than we want,” Hezel says.

At that point, Jackson can navigate back to his catalog of edgertronic camera footage, or his pitch to Harper, and parse through slow-motion releases of his pitch. This will remind him of the cues he has built this pitch on — hand position, lack of pull, not letting his head beat him.

Based on Jackson’s results through the midway point of the season, he hasn’t needed to correct much at all. He leads the Braves in saves and has become the team’s most valuable reliever in a crowded National League playoff race. Come September and October, he will be thrown into the fire in some of the highest-leverage moments of his career. The slider he built with the help of individuals like Reid Cornelius and Bill Hezel will be his main weapon. That will be the ultimate test.