Image: Charles LeClaire – USA TODAY Sports
Twenty-seven year old Pittsburgh Pirates reliever Dauri Moreta doesn’t throw a normal slider. In fact, according to the movement profiles, you’d be hard-pressed to call it a slider at all. The pitch has 12.7 inches of arm-side movement despite only 27% efficiency, and what appears to be a traditionally supinated righty slider release. It’s been fooling some of baseball’s smartest fans, and understandably so—the numbers and video surrounding the ball’s release and spin don’t correlate whatsoever with its movement. It’s a mystery. However, after looking at a slow-motion release of the ball, I have a guess.
To understand my hypothesis we’ll need a quick refresher of two terms: transverse spin, and gyro spin. Transverse spin is what makes the ball move in accordance with the Magnus effect. Many curveballs drop, fastballs “rise,” and changeups “run” because of this effect. It’s not the only reason, but it’s got a big hand in it. Gyro spin is, in essence, the “opposite” of transverse spin. As Driveline puts it, “[gyrospin] does not contribute to the Magnus force at all.”
In layperson’s terms, it’s when a ball spins like a bullet when shot, or the spin cycle of a washing machine. Although this may appear to be useless, (why do we want a pitch that goes nowhere but down with gravity?) a gyro-slider’s effectiveness often comes from its late movement. As the vector of the ball changes from straight ahead (when it leaves the hand) to down towards the catcher’s knees (as it’s approaching the plate), some of the gyro spin is converted to transverse spin. In other words, the ball begins to move gloveside.
Here’s a textbook example of a classic gyro slider:
And while this is nice, and often effective, it’s definitely not what Moreta’s pitch does. Here’s how it moves and an up-close of his release and the spin.
Go take a look at those two releases again. Notice where the dot is? The dot, as I’m informally calling it, is the axis the ball spins around. For a perfectly spun gyro-slider, that dot would be directly behind the ball. In the first pitch, it’s a bit low. This often happens with sliders, and, because of the extra tilt, can lead to more late gloveside movement.
Moreta’s dot is not directly behind the ball (splitting it) or tucked underneath it, but above the center of the ball. What does this mean?
Well, what it could mean is that Dauri Moreta’s so-called “gyro-slider” is moving opposite to the convention. Instead of dropping with gravity alone until the ball’s vector picks up transverse spin (again causing that late movement), the slider darts to the right early, before changing its vector and consequently losing its transverse spin.
Instead of moving late, and armside, it moves early and gloveside. Somehow Moreta is able to get his hand above and a bit in front of the ball and get some early armside spin before the ball drops straight down (as all the transverse spin is converted to gyro).
Regardless of whether or not my hypothesis is correct, the pitch is effective. It boasts a wildly impressive 42.1% whiff rate and has allowed an opponent xwOBA of .207. The pitch gets both whiffs and weak contact, a coveted combo. Moreta has paired it with an effective fastball and emerged as one of the league’s most underrated relief pitchers.
He has struggled with walks a bit, but the overall numbers are impressive. He has the 6th highest K% of relievers with at least 40 IP and boasts a Savant page with an impressive amount of red. And much of Moreta’s recent effectiveness can be attributed to that slider, which saw an increase in usage of almost 40% from ‘22 to ‘23.
Moreta’s future as a successful reliever is by no means certain. Neither is my understanding of his wacky slider. I am, however, certain he will keep throwing it. And I will keep watching.
(A big thanks to PitchingNinja for these videos. If for some reason you aren’t following him, change that.)
Categories: Articles, MLB Player Profiles
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