Regulating the Performance of Baseball Bats

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Regulating the Performance of Baseball Bats

• Alan M. Nathan
• Department of Physics
• University of Illinois
• a-nathan_at_uiuc.edu

• Defining, measuring, and regulating bat
  performance
• Do the regulations work?
• Recommendations

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Summary of my key points

• The current understanding of the science of bat
  performance is markedly improved
• We know how to define, measure, and regulate
• NCAA performance standards work
• Organizations should consider adopting the NCAA
  model of having an outside panel of experts to
  advise on bat performance issues

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My credentials.

• Physics professor at U. of Illinois for 30 yr
• Long career as experimental nuclear
  physicistcontinues today
• More recent interest in physics of baseball
• webusers.npl.uiuc.edu/a-nathan/pob
• Author of several papers regarding bat
  performance including
• Characterizing the performance of baseball and
  softball bats
• blueprint for how to define, measure, regulate
• Consultant to ASA, NCAA,

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Batted ball speed (BBS) in the field is the only
sensible definition of performanceThree
parameters determine batted ball speed (BBS) in
the field
My only formula BBS (BESR-0.5)vpitch(BESR0.5)
vbat

• vpitch pitch speed
• vbat bat speed
• BESR Ball Exit Speed Ratio

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BBS (BESR-0.5)vpitch(BESR0.5)vbat

• BESR a joint property of ball and bat
• Can be measured in lab, then used to calculate
  BBS in field
• with assumptions about vpitch and vbat
• All bats with same BESR that are swung
  identically will perform the same
• But not all bats are swung identically
• more on this later

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BESR depends on two additional properties of the
ball and bat

• Ball-Bat COR (BBCOR)
• The bounciness of the ball-bat collision
• Larger BBCOR means larger BESR, higher BBS
• Typically larger for aluminum than wood
  (trampoline effect)
• Bat Performance Factor (BPF)
• Ratio of BBCOR of bat to that of wood
• Moment of Inertia (MOI) of bat
• Measures weight and its distance from the knob
• Typically larger for wood than aluminum
• Affects both BESR and swing speed
• Larger MOI larger BESR, smaller swing speed
• Smaller MOI smaller BESR, larger swing speed

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Moment of Inertia (MOI) is sometimes referred to
as swing weightit depends both on actual
weight and on how far weight is from the knob
A
B

• A and B have same weight and length
• MOI of A larger than MOI of B
• B is easier to swing about knob than A

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Summary of Important Concepts

• BBS
• field batted ball speed the ultimate metric of
  performance
• BESR
• measure of performance for a given swing speed
• MOI
• affects both BESR and swing speed
• BBCOR or BPF
• affects BESR

• All of these except BBS can be measured in the
  lab
• BBS can be inferred from lab measurements, with
  additional assumptions about vpitch and vbat

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Techniques to regulate bat performance

• The direct technique
• Regulate BBS directly (ASA, fast-pitch NCAA)
• Indirect techniques
• Regulate BESR and MOI (NCAA, high school)
• Regulate BPF (LL, USSSA)

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Regulating BBS directly
BBS (BESR-0.5)vpitch(BESR0.5)vbat

• Measure BESR in the lab
• Choose typical vpitch
• ASA 25 mph for slow-pitch
• Choose vbat based on MOI
• ASA 85 mph, more or less depending on MOI
• Use equation to calculate BBS
• Reject bat if maximum BBS exceeded
• ASA 98 mph (one size fits all)

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ASA field study shows how bat speed depends on
MOI for slow-pitch softball
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Batting cage study show how bat speed depends on
MOI for college/semipro baseball players
aluminum
wood
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Regulating BBS IndirectlyThe NCAA Method

• Specify maximum BESR
• relative to wood
• Specify minimum MOI to limit bat speed
• smaller than wood
• Together, these determine a maximum BBS
• BOTH are essential to the technique

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More details on the NCAA protocol
Higher BESR, higher MOI ? same BBS
Same BESR, lower MOI ? Higher BBS
Same MOI, lower BESR ? Lower BBS
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Example 34 Bats
All bats below horizontal line and to right of
vertical line are allowed
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SummaryThe NCAA certification protocol limits
field performance of nonwood bats

• Under standard conditions---
• Wood 97 mph
• Nonwood
• Difference

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The NCAA bat compliance program has resulted in
return of offensive statistics to earlier levels
BESR
MOI
aluminum
-5 rule
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Regulating BBS IndirectlyThe BBCOR or BPF
technique

• BBS depends on two properties of the bat
• BBCOR or BPF
• MOI
• For a given BPF, the effect of MOI partially
  cancels
• Larger MOI means larger BESR but smaller vbat
• Smaller MOI means smaller BESR but larger vbat
• Therefore, ignore MOI altogether and regulate BPF
• Little League BPF
• NOTE this DOES NOT mean BBS is 15 larger than
  wood

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For slow-pitch softball bats, BPF does not track
with BBS
I do not recommend using a BPF standard for
slow-pitch softball
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Recommendations

• Become educated in bat performance issues
• Talk with the experts
• Take advantage of lessons learned by the NCAA
• Consider forming an NCAA-like panel to advise you
  on these issues
• Test broad selection of bats to see range of
  BESR, MOI, BPF,
• Do a field study to determine swing speeds, BBS,
  etc.
• From these studies, develop bat policing program

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Summary and plan for the future

• Summary of techniques for use
• Direct regulation of BBS
• Joint regulation of BESR and MOI
• Regulation of BPF
• What is best for your organization?
• Suggestion form an advisory panel similar to
  NCAA

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Summary of my key points

• The current understanding of the science of bat
  performance is markedly improved
• We know how to define, measure, and regulate
• NCAA performance standards work
• Organizations should consider adopting the NCAA
  model of having an outside panel of experts to
  advise on bat performance issues