Data is Changing Pitcher Evaluations… Total Spin vs. True Spin (simplified) – Part 3

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

Today in Part 3, we’re going to cover the topic of Total Spin vs. True Spin.  At the tail end of Part 2 (click here), we briefly reviewed how all spin is not alike, as some spin works for you to create movement and some spin doesn’t do anything at all.  At any given moment, a baseball is likely spinning along all 3 axes at the same time.  We’re talking a little bit of:

  1. Left or right,
  2. Backspin or topspin, and
  3. Spinning around in one, or the other, direction (like a football spiral spin).

However, as we reviewed earlier, the component of spin that spins around like a football and is perpendicular to the direction of travel (#3 above) doesn’t contribute to a baseball’s movement as it travels towards home plate.  And this leads us to the concept of True Spin which is a piece of data provided by the Rapsodo Baseball camera system…

True (Useful) Spin – True Spin (or Useful Spin) only reflects the components of spin that contribute to movement.  For example, a fastball may have a total Spin Rate of 2,200 rpm.  However, after a little bit of analysis, we may realize that 500 rpm of that total spin is perpendicular to the direction of travel (#3 above).  Once we remove that component, we are left with a True Spin 1,700 rpm.  Here is a visual…

Now with True Spin behind us, we can review what Rapsodo refers to as the Spin Efficiency %, which is simply True Spin divided by Total Spin.  It represents the % of total spin that is contributing to a ball’s movement.  Below is a brief summary of average Total Spin, True (Useful) Spin, and Spin Efficiency % by pitch type (source: Pitching Backward: What We Know About Spin Rate, by Jeff Long with Baseball Prospectus):

 

So, for example, an MLB curveball with an average total spin rate of 2,475 (rpm) has a True Spin rate of only 1,490 (rpm).  Only 60% of the total spin on the curveball is contributing to its movement away from its expected path.  However, it’s important to note:

“A lower Spin Efficiency % doesn’t necessarily make a pitch better or worse.”

Here is another look at True Spin % vs. Football Spin %, with the cutter having the least component of True Spin at 27% and largest component of the Football Spiral Spin at 73% (source: Jeff Long at Baseball Prospectus):

 

As every one knows, Yankee closer Mariano Rivera made a nice living with his cutter, which as pitches go has the lowest Spin Efficiency.  So, low efficiency by itself is not a good or bad thing.  It simply explains the difference between different types of pitches and gives you an important piece of data for comparing one curveball to another curveball.  

As we covered in an earlier blog (click here), it may be difficult to adjust the spin rate on your 4-seam fastball but you can certainly work to make adjustments on your secondary pitches.  Using the above table is great guideline for pitchers to assess their pitches vs. MLB pitchers, and perhaps adjust their grip / mechanics to increase or decrease spin rate / movement. The idea behind all this data is to better understand why the ball moves, what makes it move and what you can do to improve on that movement.

Please stay tuned for Part 4 where we will begin to review how to apply all this data to develop and design pitches.

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