1. Regulating the Performance of Baseball Bats
Alan M. Nathan
Department of Physics
University of Illinois
Defining, measuring, and regulating bat performance
Do the regulations work?
Recommendations
11/10/2018
Regulating the Performace of Baseball Bats

2. 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
11/10/2018
Regulating the Performace of Baseball Bats

3. Regulating the Performace of Baseball Bats
My credentials….
Physics professor at U. of Illinois for 30 yr
Long career as experimental nuclear physicist—continues 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, …
11/10/2018
Regulating the Performace of Baseball Bats

4. Batted ball speed (BBS) in the field is the only sensible definition of performance Three parameters determine batted ball speed (BBS) in the field
My only formula:
BBS = (BESR-0.5)vpitch+(BESR+0.5)vbat
vpitch: pitch speed
vbat: bat speed
BESR: Ball Exit Speed Ratio
11/10/2018
Regulating the Performace of Baseball Bats

5. BBS = (BESR-0.5)vpitch+(BESR+0.5)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
11/10/2018
Regulating the Performace of Baseball Bats

6. 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
11/10/2018
Regulating the Performace of Baseball Bats

7. Regulating the Performace of Baseball Bats
Moment of Inertia (MOI) is sometimes referred to as “swing weight”—it 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
11/10/2018
Regulating the Performace of Baseball Bats

8. 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
11/10/2018
Regulating the Performace of Baseball Bats

9. 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)
11/10/2018
Regulating the Performace of Baseball Bats

10. Regulating BBS directly…
BBS = (BESR-0.5)vpitch+(BESR+0.5)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)
11/10/2018
Regulating the Performace of Baseball Bats

11. Regulating the Performace of Baseball Bats
ASA field study shows how bat speed depends on MOI for slow-pitch softball
11/10/2018
Regulating the Performace of Baseball Bats

12. Regulating the Performace of Baseball Bats
Batting cage study show how bat speed depends
on MOI for college/semipro baseball players
aluminum
wood
11/10/2018
Regulating the Performace of Baseball Bats

13. Regulating BBS Indirectly: The 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
11/10/2018
Regulating the Performace of Baseball Bats

14. Regulating the Performace of Baseball Bats
More details on the NCAA protocol:
Higher BESR, higher MOI
 same BBS
higher BBS
MOI
BESR
same BBS
Same BESR, lower MOI
 Higher BBS
lower BBS
Same MOI, lower BESR
 Lower BBS
11/10/2018
Regulating the Performace of Baseball Bats

15. Regulating the Performace of Baseball Bats
Example: 34” Bats
102 mph
MOI limit
max vf
97 mph
BESR limit
typical wood
All bats below horizontal line and to right of vertical line are allowed
11/10/2018
Regulating the Performace of Baseball Bats

16. Regulating the Performace of Baseball Bats
Summary: The NCAA certification protocol limits field performance of nonwood bats
Under “standard” conditions---
Wood = 97 mph
Nonwood < 102 mph
Difference < 5 mph, or about 5%
11/10/2018
Regulating the Performace of Baseball Bats

17. Regulating the Performace of Baseball Bats
The NCAA bat compliance program has resulted in return of offensive statistics to earlier levels
aluminum
-5 rule
BESR
MOI
11/10/2018
Regulating the Performace of Baseball Bats

18. Regulating BBS Indirectly: The 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<1.15
NOTE: this DOES NOT mean BBS is 15% larger than wood
11/10/2018
Regulating the Performace of Baseball Bats

19. Regulating the Performace of Baseball Bats
For slow-pitch softball bats, BPF does not
track with BBS
Computer simulation
I do not recommend using a BPF standard for slow-pitch softball
11/10/2018
Regulating the Performace of Baseball Bats

20. Regulating the Performace of Baseball Bats
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
11/10/2018
Regulating the Performace of Baseball Bats

21. Regulating the Performace of Baseball Bats
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
11/10/2018
Regulating the Performace of Baseball Bats

22. 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
11/10/2018
Regulating the Performace of Baseball Bats