By: John W. Garrett

Understanding Pitch Movement Models

The Vertical Break and Horizontal Break of a pitch are vital for understanding how a pitched ball moves through the air. Whereas most pitch metrics are measured directly, such as speed, strike zone position, etc., break is a computed or “derived” metric. This means break is calculated based on multiple measured metrics using a mathematical formula or model.

The way we define and derive breaks has evolved as research continues and technology advances, providing further insights to the forces affecting pitch movement. The Pitching 1.0 and Pitching 2.0 used the Spin Induced Break model, and PRO 2.0 and PRO 3.0 report breaks using the Trajectory Break model. This article dives into Rapsodo’s past model, Spin Induced Break, and Rapsodo’s current model, Trajectory Break, looking at what these terms mean, how they differ, and why Rapsodo has moved to Trajectory Break as the model used for computing the Vertical Break and Horizontal Break of pitches.

What is Spin Induced Break?

Spin Induced Break focuses on how the spin of a pitched ball directly impacts its movement during flight.

1.     How It’s Measured:
Spin Induced Break is computed by comparing the path of the pitched ball to a theoretical path the ball would take if it were only affected by gravity and drag (i.e., without spin). This difference is attributed solely to the Magnus force, a phenomenon caused by the ball’s spin. In the event the actual strike zone position is not known (as with Pitching 2.0), the strike zone position is estimated based on the initial conditions of the pitched ball (position, velocity, and spin).

2.     Forces Accounted for in the Model:
Magnus force (caused by spin), gravity, and drag.

3.     Inputs to the Model:
Release position, release velocity, release angles, spin rate, spin direction, gyro degree, atmospheric properties.

4.     Why It’s Useful:
By isolating the Magnus force, Spin Induced Break helps us understand how a pitcher’s spin mechanics influence the ball’s movement. However, it is only able to tell us how spin affects the movement.

What is Trajectory Break?

Trajectory Break looks at the total movement of the baseball, and as a result considers all forces acting on it.

1.     How It’s Measured:
Trajectory Break measures the difference between the actual strike zone position and the theoretical strike zone position the ball would have had if it traveled in a straight line from release, only influenced by gravity.

2.     Forces Accounted for in the Model:
Magnus force (caused by spin), gravity, drag, Seam Shifted Wake (SSW), wind, and more

3.     Inputs to the Model:
Release position, release velocity, release angles, strike zone position.

4.     Why It’s Useful:
Trajectory Break provides a comprehensive view of how the ball moves from release to the plate, capturing the effect of forces that were previously overlooked in the Spin Induced Break model, such as SSW and wind.

The Key Differences Between the Models

The following image shows three different trajectories of the same pitch as a means to highlight the differences between the Spin Induced Break and Trajectory Break models.

The three trajectories represent the following:

1.     The theoretical trajectory of a pitch traveling in a straight line from release but influenced by gravity.

2.     The theoretical trajectory of the same pitch as in (1) where the movement is also influenced by the Magnus force caused by spin.

3.     The actual observed trajectory of the same pitch as in (1) and (2) where the movement is due to all forces and not limited to just gravity, drag, and Magnus.

The difference in strike zone position between trajectories (1) and (2) is the Spin Induced Break, as shown in the following image.

The difference in strike zone position between trajectories (1) and (3) is the Trajectory Break, as shown in the following image.

The key differences between Spin Induced Break and Trajectory Break are detailed in the following table.

Why Did Pitching 2.0 Use Spin Induced Break?

The Pitching 2.0 device sat between the pitcher and catcher and relied on a single camera facing the pitcher. This setup allowed for good measurements of release metrics, but the strike zone position had to be estimated as there was no camera facing the strike zone.

The Nathan Magnus model was the most physically accurate approach to estimate the strike zone position, given the understanding of the physics of ball flight at the time. Since a Magnus model (focused on spin) was used to estimate strike zone position, it made sense to report a break metric (Spin Induced Break) that aligned with this approach.

What Makes PRO 2.0 and PRO 3.0 Different?

The introduction of newer systems like PRO 2.0 and PRO 3.0 revolutionized how pitch movement is measured. These systems still sit between the pitcher and catcher but include cameras facing both the pitcher and the catcher, enabling accurate measurement of both the release and strike zone positions.

Since the strike zone position doesn’t need to be estimated, using a Trajectory Break model provides a more comprehensive view of how the ball moves from release to the plate, as it accounts for all forces acting on the ball and not only the Magnus force.

Why Transition to Trajectory Break?

Not only has Rapsodo made advancements with each iteration of ball tracking products, but Rapsodo has paid attention to and participated in ball flight research. The results of continued research and the advancements in technology have led to three key reasons to transition reporting Vertical Break and Horizontal Break using the Trajectory Break model.

1.     Broader Understanding of the Physics of Ball Flight:
Research into baseball aerodynamics - particularly work conducted by Utah State University’s Experimental Fluid Dynamics Laboratory – highlighted the importance of SSW. This research revealed additional forces, beyond Magnus, that impact a baseball’s flight.

Since Magnus is not the only force affecting ball flight, it does not make sense to define break using a Spin Induced Break model that restricts movement to just that caused by Magnus (spin).

2.     Advancements in Technology:
By employing a device that sits between the pitcher and catcher, with cameras accurately measuring both the release and strike zone positions, there is no need to estimate these metrics any longer.

3.     Fewer Uncertainties:
The Trajectory Break model relies on fewer measured metrics, reducing the level of uncertainty in the final calculation compared to Spin Induced Break model.

Conclusion: Why It Matters

As technology advances, so does our ability to measure and understand the intricate physics of ball flight. While Spin Induced Break was once the gold standard, greater understanding of additional forces affecting ball flight have led to Trajectory Break offering a more accurate representation of how pitches behave.

For players, coaches, and analysts, this shift means better tools for understanding pitch performance and optimizing strategy, and a reminder of how science and innovation continue to deepen our appreciation of the game.

Resources

• Dr. Alan Nathan Magnus Model: https://baseball.physics.illinois.edu/trajectory-calculator-new3D.html
•  "Pitched Baseballs and the Seam Shifted Wake" by Andrew W. Smith
•  "Seam Shifted Wake in the Magnus and Non-Magnus Directions" by John W. Garrett
• Rapsodo Blog: Introduction to Seam Orientation: How to Apply the Data to Pitch Desig – Rapsodo
• Rapsodo Blog: Seam Shifted Wake Effect: What Is It and Why Does It Matter? – Rapsodo
  

FAQ: Understanding Spin Induced Break and Trajectory Break

Q: What is Spin Induced Break?

A: Spin Induced Break is a derived metric that isolates the Magnus force (caused by spin) to show how spin affects the movement of a pitched baseball. It compares the trajectory of the ball to a theoretical trajectory influenced only by gravity and drag, disregarding other forces such as wind or Seam Shifted Wake (SSW).

Q: What is Trajectory Break?

A: Trajectory Break measures the total movement of a baseball by comparing its actual strike zone position to a theoretical position if it traveled in a straight line from release, affected only by gravity. This model accounts for all forces acting on the ball, including Magnus force, drag, SSW, wind, and more.

Q: How do the models differ in terms of inputs and forces accounted for?

·       Spin Induced Break: Requires more inputs, such as spin rate, spin direction, gyro degree, and atmospheric properties. It isolates Magnus force as the primary cause of movement, excluding other forces like wind or SSW.

·       Trajectory Break: Requires fewer inputs (release position, velocity, angles, and strike zone position) and incorporates all forces acting on the ball, including SSW and wind, for a more comprehensive view of pitch movement.

Q: Why did Pitching 2.0 use Spin Induced Break?

A: Pitching 2.0 relied on a single camera facing the pitcher. Since strike zone position had to be estimated using the Nathan Magnus model, it made sense to report Spin Induced Break, which aligned with this approach by focusing solely on Magnus force.

Q: How do PRO 2.0 and PRO 3.0 enable the use of Trajectory Break?

A: These systems include cameras facing both the pitcher and the catcher, enabling direct measurement of release and strike zone positions. This eliminates the need to estimate strike zone position and allows for the calculation of Trajectory Break, which considers all forces acting on the ball.

Q: Why transition to Trajectory Break?

1.     Broader Understanding of Physics: Research on baseball aerodynamics has revealed additional forces, such as SSW, that impact ball flight. Trajectory Break captures these forces, unlike Spin Induced Break, which focuses solely on Magnus.

2.     Technological Advancements: Newer systems with dual cameras provide accurate measurements of both release and strike zone positions, making Trajectory Break feasible.

3.     Fewer Uncertainties: Trajectory Break relies on fewer inputs, reducing propagated uncertainty in calculations.

Q: Why is Trajectory Break more comprehensive than Spin Induced Break?

A: Trajectory Break considers all forces acting on the ball, including previously overlooked effects like SSW and wind, providing a comprehensive view of the ball's movement. Additionally, the calculation involves fewer input metrics, reducing uncertainties compared to the Spin Induced Break model.

Q: How does understanding these metrics benefit players and coaches?

A: By transitioning to Trajectory Break, players, coaches, and analysts gain a more accurate representation of pitch movement, enabling better evaluation of pitch performance, improved strategy, and deeper insights into the mechanics of the game.

Q: Does Spin Induced Break still have value?

A: Yes, Spin Induced Break remains a valuable tool for isolating the effects of spin mechanics on pitch movement. However, it does not provide the full picture of all forces influencing the ball, which is why Rapsodo has transitioned to Trajectory Break for broader accuracy.

Q: What is Seam Shifted Wake (SSW), and why is it significant?

A: SSW is a force caused by the seam orientation of a baseball that affects its trajectory. Research from Utah State University highlighted its importance, showing that SSW significantly influences ball movement. Trajectory Break accounts for SSW, while Spin Induced Break does not.

Q: What is the Magnus Effect?

The Magnus Effect is a physical phenomenon that explains how spin influences the movement of a ball or object in flight. When a spinning ball moves through the air, the rotation creates a pressure difference on opposite sides of the ball, causing it to curve or deviate from a straight path.

Q: What is the future of pitch tracking technology?

A: As technology and research evolve, pitch tracking will continue to improve, incorporating even more precise models and metrics. This ensures that players and analysts have the best possible tools for understanding pitch performance and optimizing gameplay strategies.