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Dauri Moreta’s slider is among the best in baseball. It’s at the top of the leaderboards in several categories, and with that pitch in his bag, Moreta is enjoying a career year. There is, however, a problem with the pitch.

There’s no consensus as to whether it’s actually a slider. 

“You can call it whatever you want, but in my mind, it’s not a slider,” said Jason Delay.

“It’s still a slider. It still acts like a slider the way it spins [and] the action on it. Sometimes, it does some really, really weird things,” said Austin Hedges.

“Well … it’s a slider,” said pitching coach Oscar Marin. “But it’s more of a screwball for me.”

Moreta considers his pitch a slider. Baseball Savant classifies it as a slider. The pitch, however, does not act like a slider -- at least, all the time.

The first version -- the “normal” version -- doesn’t have a ton of horizontal movement, but looks like a run-of-the-mill slider. Here’s an example:

The second version, by contrast, looks nothing like a slider and is defined by its arm-side run. Here’s an example:

So, what’s going on here? These two same-but-different pitches fall under the umbrella of “slider” and the metrics are all out of whack. 

Moreta’s average slider averages -12.0 inches of horizontal movement compared to sliders with similar velocities and release points. That’s dead last in the league.

When Delay, Hedges and Marin were asked about the slider, there was one other pitch that all three separately mentioned. 

“The slider does have some slider traits at times, but when it’s really, really good, we see the tendency of that slider working like a screwball and actually going the opposite direction,” Marin said. 

“It’s anywhere between a slider and a screwball,” Hedges said. “It’s a legitimate screwball when he throws it a certain way; you definitely can’t call it a slider sometimes.”

Recalled Delay, “I remember the first time I caught it in Spring Training, I was like, ‘Is that a screwball? What’s going on there?’”

Delay and Hedges have caught their fair share of pitchers over the years, but neither could think of a single one who had a pitch that moved like Moreta’s slider. Marin, however, recalled Drew Smyly, whose curveball also moved in the opposite direction, making Moreta’s slider less of a surprise. 

“But that was the curveball,” Marin said. “For someone to have a slider like that, it’s pretty unique.”

Moreta learned his slider from right-hander Matt Pidich, a teammate of Moreta’s with Triple-A Louisville last season. Moreta recalled that he lost his slider at one point, but he rediscovered the pitch thanks to Pidich, practicing with Pidich just about every day.

“I honestly don’t know how he does it,” Hedges said. “It starts its way moving left, then it comes back right. It’s really wild.”

If Hedges wants an answer as to why Moreta’s slider moves how it moves, he won’t find any answers by asking Moreta himself. 

“I don’t know why it goes the opposite way,” Moreta said. “I don’t try to do that. It’s natural. I just throw it like a normal slider, and it does that.”

Delay and Hedges know to be prepared for a “slider” that might move in either direction. Delay, who also likened the pitch to a changeup and splitter due to its arm-side run, described the necessity to swallow his pride when catching Moreta’s slider. While catchers naturally want to frame, Delay and Hedges’s focus with Moreta’s slider is just catching the ball. The slider provides a unique challenge, but Delay knows that if the pitch is hard to catch, it’s also hard to hit. 

“It’s probably the most challenging pitch I’ve had to catch, certainly this year and maybe in my career because you don’t exactly what it’s going to do,” Delay said. 

“I’m not really anticipating anything about what it’s going to do, and that’s one of the beauties of being able to call it as much as we do,” Hedges said. “Even if a hitter’s looking for it, it’s not going to have consistent movement; it’s going to do something different almost every time.”

Given how the pitch grades out, Delay and Hedges find themselves catching that pitch often whenever Moreta takes the hill.

With a Run Value of -6, Moreta’s slider ranks as one of the best in baseball. Across 45 plate appearances, opponents have a .075 batting average, .100 slugging and .166 weighted on-base average against the pitch. Moreta is in the midst of a phenomenal season -- 2.01 ERA, 3.11 FIP, 33 strikeouts in 22 1/3 innings -- and the slider is a big reason why.

Considering the results, it’s not shocking that Moreta is leaning into the pitch more than ever. In 2022, Moreta’s slider accounted for 24 percent of his pitches. So far this season, by contrast, Moreta’s slider is accounting for 55.8 percent of his pitches. The Pirates are throwing more breaking balls than any team in the pitch tracking era (since 2008), and Moreta’s sudden spikes is a significant reason as to why. 

Moreta is throwing the pitch more, in general, but he’s also throwing it more to lefties.

In March and April, Moreta’s primary way to attack left-handed hitters was with his changeup; through April, Moreta’s changeup comprised 45.9 percent of the pitches he threw to lefties while his slider lagged behind at 21.6 percent. 

In May, by contrast, Moreta’s slider is accounting for 48.3 percent of his pitches to lefties while his changeup is accounting for 31.0 percent. So far, Moreta hasn’t allowed a single hit to a left-handed batter with his slider.

Moreta recalled a teammate who asked for the true name of his pitch and joked that Moreta’s slider wasn’t really a slider. Moreta will keep calling it a slider for now, but a rebrand isn’t out of the question. Regardless of denomination, Moreta won’t stop throwing the pitch anytime soon.

“This is an outlier pitch, and it’s an outlier pitch that has really good results when located in a certain spot,” Marin said. “His is completely different than anyone we have. We leaned on that pretty heavily once we saw that because we felt like, whether it’s a legit slider or now, it’s getting the results we want.”