TL;DR Seam-shifted wake, or side force, is the difference between a pitch’s observed spin and its measured spin, as detected by MLB’s recently-installed HawkEye systems. Players whose pitches exhibit this type of movement have become hot commodities, driven by a number of the more forward-thinking MLB clubs. It’s important because, depending on the type of pitch, the amount of seam-shifted wake has shown to be a significant contributor to a pitch’s effectiveness. Summary links to Red Sox pitchers’ seam-shifted wake leaderboards can be found towards the bottom of this post.
I’ve seen a bit of chatter in different threads about the profile of pitchers that Bloom has targeted, the emerging importance of spin rates and now seam-shifted wake among forward-thinking teams around the league, and how any of this might apply to Sox pitchers. I’ve spent some time deep down the SSW Rabbit Hole and hope that others might find this summary helpful…
What is seam-shifted wake?
When a ball spins a certain way and on a certain axis, there is an expectation for how it should move. However, with seam-shifted wake pitches, the air around the ball is being altered by the location of the seams (hence seam-shifted wake), which pushes it in an unexpected way. SSW refers to the additional side force movement caused by this. This is different than the Magnus force that lifts the ball and creates “ride” or “jump” causing the ball to go up higher at the plate than the batter expects.
Who discovered it?
Utah State Professor Barton Smith is generally credited with “discovering” seam-shifted wake. The Driveline guys are said to have been studying the issue separately as well around the same time, but still. Mostly Smith.
How is it measured?
MLB’s Mike Petriello framed up how to think about SSW as comparing a pitch’s “observed movement from spin direction at the plate with the spin-based movement out of the pitcher's hand.” Put another way, "how is the actual movement at the plate different from what the original spin direction would have suggested?" And yet another way (via Smith), what you want to look for in SSW is the deviation (difference) “between the spin direction and the actual direction the ball moved.”
Is it important?
MLB’s Tom Tango isolated the effect of SSW on different types of pitches’ run prevention and showed that SSW does, in fact, play an important role. In particular, for sinkers and cutters. Research continues. SSW seems to play some role in a slider’s effectiveness. As research continues, Smith believes that breaking balls will prove out as being impacted as well.
Diving a bit more into what Tango did -- he placed all pitches from 2020 to Mid-April of this season into three different bins. Bin 1 included the 25% of pitches with the MOST amount of movement, Bin 2 included pitches with the middle 50% of movement, and Bin 3 included the 25% of pitches with the LEAST amount of movement. He then looked at how effective each bin was at preventing runs per 100 pitches. What did he find (limiting here to just sinkers and cutters)?
Sinkers:
Cutters:
Who are some of the MLB leaders in SSW?
Savant has leaderboards that can be sorted by the “Deviation” between the spin direction and actual direction. They present them as clock units, which I don’t really dig, maybe that’s just me. RHP and LHP appear on opposite ends. Here are links for sinkers and cutters (you can run leaderboards for other pitches, but I know that this post is already long as shit):
MLB leaders in sinker SSW movement (min 25 pitches)
MLB leaders in cutter SSW movement (min. 25 pitches)
How do Red Sox pitchers’ seam-shifted pitches fare?
Here are leaderboards I created for our guys, for each of MLB’s pitch classifications:
Red Sox pitchers' 4-seamer SSW movement (min. 25 pitches)
Red Sox pitchers' sinker SSW movement (min. 25 pitches)
Red Sox pitchers' changeup SSW movement (min. 25 pitches)
Red Sox pitchers' curveball SSW movement (min. 25 pitches)
Red Sox pitchers' cutter SSW movement (min. 25 pitches)
Red Sox pitchers' splitter SSW movement (min. 25 pitches)
Red Sox pitchers' slider SSW movement (min. 25 pitches)
I’ve seen a bit of chatter in different threads about the profile of pitchers that Bloom has targeted, the emerging importance of spin rates and now seam-shifted wake among forward-thinking teams around the league, and how any of this might apply to Sox pitchers. I’ve spent some time deep down the SSW Rabbit Hole and hope that others might find this summary helpful…
What is seam-shifted wake?
When a ball spins a certain way and on a certain axis, there is an expectation for how it should move. However, with seam-shifted wake pitches, the air around the ball is being altered by the location of the seams (hence seam-shifted wake), which pushes it in an unexpected way. SSW refers to the additional side force movement caused by this. This is different than the Magnus force that lifts the ball and creates “ride” or “jump” causing the ball to go up higher at the plate than the batter expects.
Who discovered it?
Utah State Professor Barton Smith is generally credited with “discovering” seam-shifted wake. The Driveline guys are said to have been studying the issue separately as well around the same time, but still. Mostly Smith.
How is it measured?
MLB’s Mike Petriello framed up how to think about SSW as comparing a pitch’s “observed movement from spin direction at the plate with the spin-based movement out of the pitcher's hand.” Put another way, "how is the actual movement at the plate different from what the original spin direction would have suggested?" And yet another way (via Smith), what you want to look for in SSW is the deviation (difference) “between the spin direction and the actual direction the ball moved.”
Is it important?
MLB’s Tom Tango isolated the effect of SSW on different types of pitches’ run prevention and showed that SSW does, in fact, play an important role. In particular, for sinkers and cutters. Research continues. SSW seems to play some role in a slider’s effectiveness. As research continues, Smith believes that breaking balls will prove out as being impacted as well.
Diving a bit more into what Tango did -- he placed all pitches from 2020 to Mid-April of this season into three different bins. Bin 1 included the 25% of pitches with the MOST amount of movement, Bin 2 included pitches with the middle 50% of movement, and Bin 3 included the 25% of pitches with the LEAST amount of movement. He then looked at how effective each bin was at preventing runs per 100 pitches. What did he find (limiting here to just sinkers and cutters)?
Sinkers:
Just to summarize what we’re seeing here -- for sinkers, those with the most SSW movement prevented runs at almost twice the rate (-0.41) as sinkers with the best overall movement (-0.22)Total Break:
1 [most movement]. -0.22
2 [middle]. +0.08
3 [least]. +0.46
Magnus:
1 [most movement]. +0.07
2 [middle]. +0.05
3 [least]. +0.51
SSW:
1 [most movement]. -0.41
2 [middle]. +0.37
3 [least]. +0.36
Here we see that the story of the Sinker is all about the SSW (or more technically the non-Magnus force, which we are presuming is the SSW).
The sinkers that are getting the most SSW are by far the most effective.
Cutters:
Pretty amazing. Just look at how effective the 25% of cutters with the most amount of SSW movement are at preventing runs (-0.61) relative to the same class of pitch with different movement characteristics.Total Break:
1 [most movement]. -0.01
2 [middle]. +0.23
3 [least]. -0.29
Magnus:
1 [most movement]. +0.13
2 [middle]. -0.32
3 [least]. +0.45
SSW:
1 [most movement]. -0.61
2 [middle]. -0.02
3 [least]. +0.58
Here, the cutters finally make sense, because of the SSW. If we just look at total break, the most effective cutters are those that have either the most or the least amount of break, with the least amount of break winning. In other words: a slow non-breaking fastball. Which is… odd.
If we look at the Magnus force splits, the conclusions are even more confusing. So, we learn nothing (or less than nothing, negative nothing) by looking at the Magnus splits of cutters.
Ah, but SSW on Cutters, that’s where it happens: by far, the cutters with the most SSW are the most effective, and those with the least amount of SSW are the least effective. Finally, we get to see some explanation for how to measure the effectiveness of cutters and it lies with the SSW.
Who are some of the MLB leaders in SSW?
Savant has leaderboards that can be sorted by the “Deviation” between the spin direction and actual direction. They present them as clock units, which I don’t really dig, maybe that’s just me. RHP and LHP appear on opposite ends. Here are links for sinkers and cutters (you can run leaderboards for other pitches, but I know that this post is already long as shit):
MLB leaders in sinker SSW movement (min 25 pitches)
MLB leaders in cutter SSW movement (min. 25 pitches)
How do Red Sox pitchers’ seam-shifted pitches fare?
Here are leaderboards I created for our guys, for each of MLB’s pitch classifications:
Red Sox pitchers' 4-seamer SSW movement (min. 25 pitches)
Red Sox pitchers' sinker SSW movement (min. 25 pitches)
Red Sox pitchers' changeup SSW movement (min. 25 pitches)
Red Sox pitchers' curveball SSW movement (min. 25 pitches)
Red Sox pitchers' cutter SSW movement (min. 25 pitches)
Red Sox pitchers' splitter SSW movement (min. 25 pitches)
Red Sox pitchers' slider SSW movement (min. 25 pitches)