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Pitching’s Newest Fever: Seam-Shifted Wake and the “Sweeper”

Picture of Seam-Shifted Wake; Photo via Barton Smith and Utah State University

Of all the great advancements that came from the advanced technology we now have to better understand baseball, improved pitch design has to be both one of the most complicated and fascinating. Players are now able to throw pitches that seemingly shift like a Blitzball, curving in varieties that other generations would’ve thought were nearly impossible. But with the new tracking data and a deeper understanding of the concepts behind a baseball’s movement, these pitches can now be created and utilized at the expense of MLB hitters. One of these advancements is the sweeping slider, commonly referred to as the “Sweeper”. Arguably one of the deadliest pitches in baseball, the pitch is caused by seam-shifted wake - a physics term that will be elaborated upon. Before I dive in, I want to warn the reader that this is a relatively complicated topic that involves a lot of science-related phenomena. I will do my best to explain this phenomenon in the simplest (yet detailed enough) way possible to ensure a comprehensive understanding.

To better explain this magnificent Sweeper, it needs to be shown. Pictured below is an example of this pitch thrown by Clay Holmes, who has arguably seen the most success using the Sweeper.

As can be seen, the ball arguably “sweeps” across the plate, justifying its namesake. The action on this pitch is much better than the traditional slider. The only downside is velocity, with the Sweeper going about 3.2 MPH slower on average than the traditional slider in 2021. Yet, speed was never the point of an effective slider - last year's data suggests the Sweeper spins 125 more RPMs than the regular version of this pitch. This causes more break, with the regular slider breaking 7 inches horizontally and the Sweeper breaking 15 inches (a roughly 114% improvement). But while spin is important in some cases, the deadliness of this pitch is not entirely caused by the high spin rate. It is owed to a newer scientific concept that is breaking the way physicists think of pitching.

Introducing Seam-Shifted Wake - the cause of this absurd pitch. Originally discovered by Alan Nathan using Pitch F/X Data (the private version of MLB data before Statcast), he found that the degree of late movement that certain pitches have are not owed to the regular concepts of pitching. To properly explain this, I will attempt to boil down the science behind the concept, as I believe knowing that is incredibly important in understanding how this pitch is physically possible. When a regular pitch is thrown, it is usually subject to a “Magnus” effect - a pitch moves based on how the ball is being held and the slip of the fingers behind the spin. Regular pitches are under the influence of this effect, spinning in the same manner from the pitcher's hand to the plate, moving as when the ball left the hand. The Sweeper, and other pitches that are prone to seam-shifted wake, are not limited to this Magnus. Instead, they experience a state of Non-Magnus. When under this state, a pitch can gain free movement, curving and moving in ways that didn’t come originally from the hand grip. In a sense, the ball appears to be moving on its own. But it’s not - it’s experiencing a heavy dose of Seam-Shifted Wake.

To grasp this, I have provided another example of this absolutely phenomenal pitch, except by Dodgers pitcher Andrew Heaney.

When you view the video, it becomes more and more obvious that the pitch movement just appears on the scene, with absolutely no warning. Batters’ brains are making the thousands of mini-calculations of the ball's movement, utilizing what they’ve seen before to swing at its location. Except, the pitch is not going where it should. The calculations were for nothing, as the ball went in the opposite direction. Now, this is where Seam-Shifted Wake comes in. On a regular pitch, the air around the ball smoothly goes around and flows with the seams, undergoing the aforementioned Magnus effect. But what happens if you throw the ball just right to have the seams interrupt the regular airflow? What happens when the seams shift? In simplified terms, when the air pressure sticks around the shifted seams, a break in that pressure causes the airflow to suddenly go to the left or right of the ball (depending on a couple of factors). This breaks the regular pattern of wake, which is the airflow that one would see rippling after a moving object. The sudden new airflow pushes the baseball in the opposite direction horizontally, causing the pitch to break just enough in a way that wouldn’t be expected. As I know words can be sometimes too difficult to visualize, I’ve linked a great video that, while a bit more complicated, will provide a clear visual of how this pitch comes to be.

While knowing the science behind this pitch is quite interesting, it is only useful if the results of such a noted phenomenon are distinct from a regular pitch. The industry-leading private pitch designer Driveline Sports was able to track the difference in pitches due to non-Magnus effects (Seam-Shifted Wake), allowing fans to see the value-added from this phenomenon. Using their version of a statistic called Stuff+ (which factors the value of velocity, break, angle, and extension of a given pitch, using 100 as average), they calculated that the average Slider has an additional 7.6 points due to non-Magnus effects. Ergo, sliders like the Sweeper that utilize a more non-Magnus approach do benefit from its effects. They also concluded that, while non-Magnus effects added value to the pitch, it was not much in comparison to the cutter, which had 32.5 additional points due to non-Magnus effects. They did admit that this conclusion did not account well for late break, which the Sweeper is appropriately known for, due to their given data at the time. Hence, their conclusion could’ve misjudged the effectiveness of the pitch. While I am unaware of how much their conclusion could be off, it does suggest that further research needs to be done to examine the actual value of the Sweeper.

The science behind this type of pitch design is continually growing, with the industry's best and brightest working on new and innovative breakthroughs. The baseball community may not have all the answers, as most of these types of analytics have only popped up publicly within the past few years. Yet, I am optimistic about the future of both the analytics tools and the Sweeper itself. As I’ve mentioned in past articles, the breadth of analytical knowledge in baseball has been growing exponentially, providing new and never-before-seen ways to evaluate players. Thus, more exciting improvements with the Sweeper should be expected.

The Sweeper continues to be incredible to watch, completely confusing batters. Over time, I imagine that extensive data will prove its effectiveness over traditional options. After all, it does break roughly 8 more inches horizontally, making it theoretically harder to hit. By purposefully being designed to take advantage of the advanced physical concept of non-Magnus (Seam-Shifted Wake), it is hard to imagine a world where its value is not well-above a traditional slider. It may take time to ultimately get an answer, but for now, continue to look on in amazement at the feats pitchers can now accomplish. We are in a new age, and we should be embracing it to the fullest.



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