In Game 3 of the Twins/Astros ALDS, the subject of Sonny Gray’s Sweeper came up in the broadcast booth. That set the stage for Adam Wainwright to clear up some confusion that dates back a ways, and put forth an answer to the question that has been spinning around the league for a while: What exactly is a sweeper?

Here’s the clip:

Adam Wainwright explains the difference between a sweeper and a Slider ? pic.twitter.com/vdtCh9EU6W

— FOX Sports: MLB (@MLBONFOX) October 10, 2023

In just over a minute (and with deftly added pauses for the purposes of game calling), Wainwright covered a lot of ground, first pointing out the shape of the sweeper as compared to a traditional slider, then going on to scratch the surface of how the pitch is thrown and how that impacts its shape. At one point during his spiel, he chuckled at the camera, visibly concerned about how little time he had to explain something so complicated. So with the benefit of a much more flexible word count than he was afforded in the booth, let’s break down Wainwright’s breakdown, beat-by-beat, and see if we can illustrate and expand on what he was talking about by taking a look at some of 2023’s sweepingest pitchers.

Wainwright begins by describing the sweeper’s ample horizontal movement, perhaps the most easily clockable difference between a sweeper and its breaking Ball brethren. He mentions that Gray’s sweeper averaged 15.5 inches of horizontal movement (Baseball Savant has it at 15.6), which is several inches more than the league average sweeper movement, which itself is higher than the average slider. Of course, pitchers have been exceeding those slider averages since the days when the Minnesota starter was more Sonny than Gray, and indeed, long before that. But with the recent proliferation of breaking balls that hardly resemble the sliders of yore, the terms slurve and sweeper were officially added to MLB’s lexicon in order to better distinguish how these breaking balls are used and thrown.

According to Savant, the pitcher who ranked the highest in average horizontal movement on his sweeper in 2023 was veteran Rich Hill, whose season average was a whopping 21.3 inches of glove-side movement. Hill also occasionally throws a traditional slider, so let’s take a look at those two offerings and see how they differ.

Here’s a side-by-side of a sweeper and a slider that Hill threw back in late April:

The difference between those pitch shapes is easy to see, but the numbers that describe the shapes are murkier than Wainwright’s brief description may have made them seem. Hill’s 64.8 mph sweeper had 23 inches of horizontal break, well above the averages sited by Wainwright. But his 75 mph slider clocked in at 14 inches of glove-side movement, which falls within the range of what Wainwright described as a sweeper (on the high end, in fact). It would be nice if a pitch registering that much glove-side movement could automatically be classified as a sweeper, but that would be too convenient. And as Hill’s arsenal alone demonstrates, it would be somewhat misleading to lump the two pitches into the same category in terms of his respective usage of them. In truth, Hill throws both pitches with above-average movement — the difference that qualifies one as a sweeper and the other as a slider has to do with how they’re thrown. In Hill’s case, his arm slot is significantly lower when he throws the sweeper than when he throws the slider:

This lowered arm slot, likely in conjunction with a grip adjustment, allows Hill to alter the spin on the sweeper by moving its axis of rotation to the top of the ball, as opposed the ball rotating around a more front-facing axis when he throws the slider:

Hill’s arsenal is deep enough that he can get away with this release point variation. He releases his slider from a spot similar to his four-seamer and curveball, while his sweeper release is similar to that of his sinker, so even if a batter clocks the different slots, he still has some guessing to do:

Many pitchers who throw sweepers do so from an extreme sidearm release point, which makes sense; the further a guy reaches his arm out horizontally, the more of a horizontal angle he can create with the ball’s path toward the strike zone. It stands to reason, too, that throwing from such a low arm slot would aid in creating that hurricane-like sideways spin. Ranking second behind Hill in terms of average horizontal movement was Greg Weissert, whose sidearm release points are much more consistent across his pitch mix:

In Weissert’s case, he throws a sweeper instead of a traditional slider, with his low release point aiding its slingshot effect. His sidearm is a headache-inducer for right-handed opponents, while his effectiveness against lefties depends on his ability to pair his sweeper with a changeup he throws from the same arm slot but with wickedly different movement:

Not all sweeper-throwers rely on a sidearm release to create lateral action, though. Third on Savant’s list of the most horizontal sweepers was Tampa Bay’s Jason Adam. He throws from a higher three-quarters arm slot, but he still created an average of 20.4 inches of glove-side movement on his sweeper. That’s nearly double the horizontal action of the slider he was throwing when he was still with the Cubs a couple years ago, though his arm slot has remained relatively the same.

Here’s what it looked like in 2021:

And here’s where he was releasing his pitches in 2023:

The increase in horizontal movement without an exaggeration of his arm slot implies a subtler change. This could be any number of things, especially given the Rays’ reputation as a spin-savvy org. Here’s what Adam’s bygone slider looked like in 2021, compared to the sweeper he’s slinging nowadays:

While the camera angles here are too different to allow a fair comparison of these pitches’ respective shapes, there are a number of mechanical alterations that hint at how Adam has added horizontal movement to his breaking ball. For one, he now has a markedly shorter arm action, with his arm barely dipping below his right shoulder as he brings it behind his body at the start of his delivery. He also now finishes his delivery with his thumb pointed up, suggesting an upward facing palm upon releasing the pitch – a “supinated release,” as Spencer Strider once described it to a seven-year-old – as opposed to the more downward-facing palm and thumb (pronated release) in his 2021 follow-through.

Here’s that same video, but with freeze frames showing Adam’s shorter arm action, and the position of his hand during his follow-through:

While this video is shot from too far away to confirm it, another likely change may be his grip on the ball. With that in mind, let’s get back to Wainwright in the ALDS booth.

After describing the horizontal shape of a sweeper, Wainwright gave a brief description of some key characteristics of a traditional slider. “When you throw a slider,” he explained, “you’re going to see a red dot.” Here, he’s describing the effect of the gyroscopic, football-like spin that a pitcher applies to a slider, spinning it clockwise or counterclockwise as it makes its way to the plate. When a ball with that type of spin is flying toward a batter, a red dot appears on the ball, created by the red seams at the ball’s axis.

Here’s an example in ultra-slowmo from Jacob deGrom, whose slider features an average of just five inches of horizontal movement. From this angle, you can see the red dot:

Here’s a close-up of the ball, with the colors adjusted to better make out the seams:

Wainwright went on to describe how a sweeper differs from a slider like deGrom’s, rotating the ball he was using to indicate specific seams and assuring the audience that “there’s some science behind this,” before pausing to watch Jose Altuve foul a ball into the left field stands.

The science he’s referring to is seam-shifted wake, which broadly describes the aerodynamics of a baseball in motion, the wake the ball’s seams create as it flies through the air, and how that wake can inform the optimal way to throw a given pitch. Wainwright’s truncated primer on the subject had to do with the seam orientation of a breaking ball when a pitcher releases it and how it can be used to the pitcher’s advantage in terms of “catch[ing] the air,” as he phrased it. He indicated that when throwing a sweeper, the aim is to release it with a seam near the top of it, angled in such a precise way as to use the air around it to create more horizontal action, similar to what Rich hill’s spin animation demonstrated above. As Wainwright described this, he wiggled his finger, illustrating a frisbee-like twirl as the ball flies through the air.

Here’s some footage of Shohei Ohtani, whose sweeper’s average horizontal action in the mid-teens was similar to Gray’s in 2023:

There’s still a red dot, but now it’s almost on top of the ball, creating that revolving-door-like rotation:

This has largely to do with the seam orientation of the ball, along with his hand and arm motion as he releases it. In deGrom’s case, his slider grip is a more traditional one. When the ball leaves his hand, his fingers are behind the ball, with two vertical seams facing the batter:

Ohtani’s hand is positioned with his fingers on the side of it, with the seamless face of the ball facing the batter and the seam that Wainwright had previously pointed out oriented across the top of the ball. The way Ohtani aligns his fingers with the seams is more akin to a traditional two-seamer than a slider, but by throwing it with this type of supinated release, he changes the movement created by that finger placement:

Wainwright concluded by saying that the sweeper’s effectiveness lies in its ability to subvert the expectations of batters who are used to breaking balls looking a certain way by throwing a familiar-looking offering that ends up several horizontal inches away from where the hitter is expecting it. I think my favorite part of Waino’s explaino is when he sums it up with “It’s just weird,” which is as definitive a note to end on as one can expect after delivering a Cliff’s Notes approximation of a concept that is constantly evolving.