Data is Changing Pitcher Evaluations… Putting Analytics to Work – Part 2

By Robbie Aviles (RHP Cleveland Indians, Pitching Lab Coach)
Bahram Shirazi (BSEE, MBA, Co-Owner RPP)

In Part 1 of this series, we wrote about how data and analytics provided by new equipment such as Rapsodo Baseball cameras is changing the way pitchers are getting evaluated and trained.  In Part 2 and Part 3, we’re going to dig a little deeper into:

  • What it (spin) all means,
  • How movement is generated,
  • Different types of spin and related info,
  • Advantages of having access to the data,
  • Why it’s important to understand the ramifications, and
  • How we can use it to our benefit.

With that said, let’s go over some basics.

Competing Forces on a Baseball – A baseball on its way to home plate can get tugged in several directions, all of which effect its trajectory and movement.  These forces obviously include gravity, air resistance, and the velocity with which it was thrown.  However, it’s also impacted by Magnus Force.

Magnus Force – Magnus force is all about the pressure around the baseball that creates a deviation from its “expected” path by creating what everyone refers to as “movement”.  It is a phenomenon associated with a spinning baseball that drags air faster towards one side.  This in turn creates a difference in pressure that moves the baseball in the direction of the lower-pressure side.  Below is an example of Magnus Force created on a fastball (backspin) heading towards a batter from a side view.

The backspin of a fastball:

  • Increases ↑ air pressure under the ball,
  • Reduces ↓ air pressure above the ball, and
  • Creates a Magnus Force that puts upward movement pressure on the ball.

Conversely, a curveball (forward spin) would create a Magnus effect downwards.  Hence the “curve” in the curveball arcing downwards.  You could say that without dear old “Magnus” the game of baseball wouldn’t be the same.

Spin Rate – A baseball on its way to home plate spins along at multiple axes at any given moment.  From the pitcher’s perspective, this includes A) side-to-side, B) forward or backward and C) around, similar to Daisuke Matsuzaka’s infamous gyroball (like a football spiral).  In reality, baseballs have spin along all 3 axes at the same time (we’re talking a little of “left or right”, a little of “backspin or forward spin” and a little of “around in either direction”).

Just in case you are wondering what a pure “Pitch C” looks like, here it is, Dylan Bundy’s slider/gyro (observe the dot on the back of the baseball after release, need a desktop computer to really see it):

(Dylan Bundy’s Slider and Spin, Courtesy of Pitcher List)

Spin Axis – The axes of spin (dashed red lines in the images below) combined with the spin rate are the true culprits in creating what we call “movement”.  Although, rarely is a baseball thrown 100% along a single axis, the images below provide a visual of each axis (visualize the ball is heading towards you):

It might surprise you, but all spin is not alike, as some of the spin works for you to create movement and some of it doesn’t do anything at all.  For example:

  • The ball on the left, will have movement to the left or right, as Magnus Force pulls it in one or the other direction,
  • The ball in the middle, will have movement up or down, as Magnus Force pulls it in one or the other direction, and
  • The ball on the right (the gyroball spinning like a football heading towards you), will have NO Magnus Force working on it and therefore NO additional “movement” in any direction.

Yes, you read that correctly.  “C” does nothing for creating movement because gyrospin generates no Magnus Force on a baseball. A lot of folks have a hard time with this one, but if you think of the spin around a true gyroball as being 100% perpendicular to the direction of travel, then you can assume with 100% certainty that the pressure created around the baseball from this type of spin is identical on all sides.  Visualizing it might help.  Imagine the spinning baseball in the image below coming towards you with the yellow axis in the center of the ball pointed directly to you.   The net result of the Magnus Force (around the baseball) in this specific instance is zero as the air pressure on all sides depicted by the red arrows is identical.  This baseball will have no movement on it from its expected path.

And this brings us to the topic of True Spin or Useful Spin.

Stay tuned for Part 3 where we will begin discussing True Spin data coming out of the Rapsodo Baseball camera and how you can put this type of information to work in helping with pitch design and development, among other topics.

Sign-up for Future Blogs (3)

Facebooktwittergoogle_plusredditpinterestlinkedintumblrmail

Trackbacks

  1. […] The Hardball Times examines The Physics of RoboUmp. Robbie Aviles and Bahram Shirazi’s Spin Rate Analytics Simplified. Bill James starts his look at the best third baseman of all time (part 1 and part 2). Tom […]