Introduction
During the pandemic lockdowns, I stumbled upon Barton Smith’s blog about the fluid dynamics of baseball pitches. It inspired much of my effort to understand the true behavior of baseball trajectories. I’ve wanted to write about this for over four years, but life (i.e. my day job and family), kept me busy. More importantly, I kept postponing it because I was waiting to “figure it all out” perfectly. I’ve now realized that perfection is an impossible goal. So I’ve decided to document my journey and share my thoughts before I forget or lose interest in this captivating topic. I am starting a sabbatical in June, and this should finally give me the time to organize all the ideas and simulations that have been accumulating on my hard drive and in my notebooks for years. I will try to add to this series roughly once a month as I continue experimenting, running simulations, and learning new things along the way.
Before diving into the topic, I should confess that I’m not an aerodynamicist. My expertise lies in astrophysics, particularly in modeling stellar atmospheres. Until my recent foray into baseball aerodynamics, I had never worked with Navier-Stokes equations or encountered concepts like boundary layers and other related phenomena. To understand these, I had to teach myself from scratch. Along the way, I became good friends with Professor Barton Smith, Mr. Seam-Shifted Wake himself, and even collaborated with him on a paper about this fascinating subject.
Prior to that, I had created a VPython version of Alan Nathan’s trajectory calculator, incorporating state-of-the-art modeling for drag and Magnus forces. As someone who pitched during my youth (not at a professional level, my 5’8″ frame and poor mechanics capped my velocity at around 80 mph), I always felt there was more to baseball movement than what traditional models accounted for. My arsenal included a nasty sweeper and an uncatchable knuckleball, though the latter only worked about one in four attempts. So even before I became a physicist, I always felt there was more to pitch movement than just the Magnus effect, but I could never quite put my finger on what it was until I came across Barton Smith’s blog.
What is Seam-Shifted Wake?
The term seam-shifted wake (SSW) has gained traction in recent years, thanks primarily to Professor Barton Smith and his students at Utah State University. In brief, it refers to an additional aerodynamic force on a baseball, beyond gravity, drag, and Magnus forces, arising when the ball’s seams are positioned in a particular way. This force significantly influences the trajectory of many pitches, and is most apparent for sinkers, sliders, cutters, sweepers, changeups, and of course knuckleballs.
Pitchers have long known how to manipulate the ball’s movement with grip and seam orientation. Expressions like “the wind catches the seams” or “airflow comes into play” are common among professionals. Here’s the colorful Bill « Spaceman » Lee explaining how sinkers work:
While pitchers have intuitively understood these effects for decades, it’s only recently that scientists have begun to formalize and explain the phenomenon. Barton Smith has extensively documented the subject on his blog, providing excellent explanations of SSW. However, many online descriptions of SSW/seam effects are either incorrect or oversimplified (for example this one, and this one) or lack practical applicability. This is understandable, given the complexity of the topic and how our understanding has evolved over time. In fact, anyone claiming they have completely figured out seam-shifted wake is either lying or delusional. As we will see, there are still many loose ends and lingering uncertainties, and there probably will be for several years.
What Can You Expect from This Series?
If you’ve read or listened to everything Dr. Smith has published, my explanations may not offer much new information. However, even a motivated individual who has done their homework might find themselves with a general understanding but no clear path toward actually applying the knowledge to improve pitches. My goal here is to bridge that gap by approaching the topic a bit differently in two key ways:
- Deeper Physics Exploration:
I’ll delve into the physics of SSW in more detail. Understanding the underlying principles provides a stronger grasp of what’s happening and allows for more quantitative analysis. - Practical Tools and Simulations:
Along the way, I’ll provide 3D visualization tools and, ultimately, I will share my trajectory simulator that includes SSW. These resources should help anyone interested understand which variables matter most for controlling pitch movement.
By the end of this series, you should have a better understanding of why your two-seamer doesn’t sink, how to grip the ball for specific effects, why a grip works for pitcher X but not for you, how Ohtani’s splitter can move in two different directions, why Japanese or high school baseballs behave differently, how wind influences all of this, and more. Many players, including professionals, don’t fully understand all the science behind seam-shifted wake that I am about to discuss, but they have learned how to use it and benefit from it. Hopefully, by the time I’m done, seam-shifted wake will start to look less like black magic and more like something you can actually predict, control, and use on purpose.