Seam-Shifted Wake on Gyro Sliders: A Hypothesis

*Skip to “The Unexplained Gyro Slider” if you don’t need the introduction*. That’s where you’ll see the Seam-Shifted Wake talked about.

It’s been more than a decade since pitch f/x data emerged onto the baseball community. Since then, we were able to analyze the velocity & movement of the pitchers’ arsenal, and tell the story of how someone’s Curveball is the best.

Up until 2020, we had access to these:

• Pitch Velocity(y)
• Release Point(x,y,z)
• Vertical/Horizontal Movement(x,z)
• Vertical/Horizontal Location(x,z)

With these data, we could calculate things like approach angles(pitcher attack angles), or pitch tunnel metrics. Some people even came up with pitch performance models like Jake Mailhot’s Stuff+, or Ethan Moore’s Quality of Pitch.

Now, how much of a pitcher’s stuff could these models explain?

Most of it.

Josh Hader’s Fastball? High Vertical movement and low Release point.

Blake Snell’s Curveball? High Velocity and Release point.

Kyle Hendrick’s Changeup? Velocity gap and Pitch tunneling.

Seam-Shifted Wakes

Up until a few years ago, pitch movement was believed to be mostly(as in almost 100%) influenced by the magnus force on the ball; in other words, spin.

The magnus model is plain and simple: More active spin = More movement. But some people suspected it wasn’t enough.

Oftentimes people noticed an unusual movement on a pitch; a pitch’s movement not aligning with the spin axis. In 2012, physicist Alan Nathan first discussed the laminar effect on the trajectory of a baseball.

The mechanism wasn’t entirely clear, until a couple years ago, when (Mechanical and Aerospace Engineering) professor Barton Smith introduced the idea of Seam-Shifted Wakes on his blog. (You can find out more in his blog.)

SSW Movement is deemed late break, and that does not clearly show up on the pitch movement metrics on the pitch f/x or Statcast data.

But now we know. Most Sinkers & Changeups use SSW in order to move more. (You can find the Magnus-Actual Movement deviation data here.)

Now, how much of the unexplained pitches could SSW movement explain?

(Almost) All of it.

The best example is Kyle Hendricks’ Sinker. His supposedly-horrible pitch profile on his Sinker(87mph, 1:00 spin axis), is combined with one of the most SSW Movement of all MLB Sinkers.

SSW allowed to explain the following pitches:

• Sink/Run on most Sinkers
• Sink/Run on most Changeups
• Knuckleballs
• “Floating” on some Sweeping Curves(Or Lateral Sliders)
• Cut on some Fastballs

The Unexplained Gyro Sliders

If there’s one pitch that hasn’t yet been fully explained by the modern theory of pitch performance, that would be the Gyro Sliders.

Not all of them, some of them. Most Gyro Sliders can be explained by their final movement(no movement). They generally perform less effectively compared to the harder versions(Hard Sliders) or the moving versions(Hard Curveballs). But some of them perform spectacularly. With no clear reason.

These sliders typically have:

• Seemingly typical movement(~3in Horizontal ~0in Vertical)
• More-or-Less vertical contrast with the fastball(~2:1 V:H)
• Slightly below-average velocity (~10 mph)

They just seem too normal. And I believe they aren’t.

Because pitchers have made careers out of them.

Patrick Corbin’s Slider

This is probably the most prominent case, so I’ll use it as an example.

Below is his 2019 Slider performance:

• 52% Whiff ~ 5th for Sliders swung at least 200x
• 30% Putaway ~ 8th for 2-strike Sliders thrown at least 200x
• .203 xwOBA ~ 4th for Sliders thrown at least 500x

Amazing. The more amazing part is that most of the pitchers above also throw the same type of Slider.

Below is his Slider profile, according to Baseball Savant:

• 81.7mph ~ -3* vs. Average
• 42.8in Drop ~ +1.1 vs. Average
• 3.6in Break ~ -2.4 vs. Average

Fairly normal. How about the contrast profile? For comparison, I’ll use Walker Buehler who has a very similar contrast on his slider.

	Patrick Corbin	Walker Buehler	*Corbin(SI)
Velocity Difference	10.1mph	10.1mph	10.0mph
V.Movement Difference	24.9in	26.3in	20.5in
H.Movement Difference	12.5in	15.9in	18.3in

*Note that Corbin has a 1/2 ft higher Release point, and Buehler throws his Slider 5mph harder.

Pretty similar. If anything, Buehler has “better” movement…besides the fact that his Whiff% was 20% lower, despite throwing it to the same location.

And I’m here to argue that Corbin’s Slider is a Seam-Shifted Wake pitch.

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Seam-Shifted Wake Offspeed?

While I was playing around with the Pitch Spin Visualizer, I found an interesting orientation on the Slider.

Here’s a seam orientation that enables the most seam-induced early separation:

*The left diagram comes from Diagram 7 of source.

1/2 of all hemisphere line on the ball is covered at all times.

That obviously wouldn’t add any extra break; there would be a bigger wake on both sides of the ball, at all times, countering each other.

Although, the total wake volume will be bigger in general.

Drag slows down the ball….

If I increase the size of the wake, there’s going to be more drag…

Does that mean I can throw an 80MPH PITCH THAT’S LIKE 75MPH?

THE ULTIMATE OFFSPEED???

YES. The ball slows down more…

…by less than 1mph.

Numbers: Drag reduces velocity so that mean velocity, which affects batter reaction time, is 4-5% lower than release velocity. Suppose SSW increases drag by 20%, which would be huge. That would change average velocity by no more than 1%, or less than 1 mph. https://t.co/3v79suXrcI

— Alan Nathan (@pobguy) January 20, 2021

That didn’t work. Let’s try again.

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Separation Point

It surprised me when I heard that SSW is extremely common in Two-seamers. I can’t wrap my head around it, since a typical two-seam orientation would affect both sides of the wake:

From the perspective of a non-physicist, this is an indication that the separation point may in fact lie more than 6° in front of the hemisphere. If not, then two-seamers with less than 45° of standard-gyro(aligned with forearm supination) should have the opposite effect of what it does; there would be an early separation on the armside, not the gloveside, or none, if the map was true.

Given that’s true, what can we do with it?

Use them on Gyro Sliders.

Reverse Gyro Sliders

100% of Sliders come with a significant amount of gyroscopic spin. And the gyro tilt has been known to be either complete gyro(pure gyroball), or a supine tilt:

And in my observations, I have seen the reverse. Some Sliders have reverse-gyro.

Why wouldn’t they show up on Baseball Savant?

If Seam-Shifted Wake adds movement onto the pitch, it should be moving more than a typical pitch. But it doesn’t.

Likely because reverse-gyro also causes reverse-movement when it comes to magnus force.

Gyro Sliders generally have a spin axis between 6:00-12:00(RHP), mostly around 9:00. Reverse-gyro Sliders have a spin axis between 12:00-3:00, which means that the movement goes in the same direction as the fastball.

That isn’t too significant(magnus-wise) when the spin efficiency is <20%. The reverse-gyro Slider would “move less” by <10 inches.

And that would be noticeable on the data. Except, the SSW reverse-reverses the movement, making it seem like nothing happened. Also, Hawkeye hasn’t been consistent/precise enough to show accurate spin axis data on the low-efficiency Sliders.

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Making Improvements

I’m not sure what the best seam-alignment would be for the most SSW movement on these Sliders. The one below could be a potential step forward:

It’s a modified One-seam Slider with (theoretically) the most amount of top wake. Although, it’s unclear how much of the wake is created at the bottom.

More Gyro

As we know, a pitch’s spin axis changes throughout its trajectory. When it comes to the sliders, the axis tilt is around 5-10°(essentially rotating backwards like a fastball).

We can use that to create late break; have the SSW effect act on the ball in the middle of its trajectory.

It seems to me that there is a big room for optimization for this Slider type, although maybe not as extreme as this one:

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Conclusion

After all of this, it’s still unclear as to whether this pitch type could even exist. Seam-Shifted Wake is still a semi-explored territory, and the physics is difficult.

Nevertheless, if this pitch does get proven correct, then we would finally be able to explain the mystery of exceptional sliders in baseball.

If there is an error in this post, please point it out in the comment section, or contact me.

UPDATE: There is a new, modified hypothesis that aligns with the current-understanding of Seam-Shifted Wakes.