Transcript Baseball and Bat Performance Standards

Regulating the Performance of
Baseball Bats
Alan M. Nathan
Department of Physics
University of Illinois
[email protected]
• Defining, measuring, and regulating bat
performance
• Do the regulations work?
• Recommendations
7/16/2015
Regulating the Performace of
Baseball Bats
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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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Baseball Bats
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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, …
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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
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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
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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 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
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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+(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)
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ASA field study shows how bat speed
depends on MOI for slow-pitch softball
Bat Speed at 6" Point vs. MOI
1.06
y = m1*(9000/m0)^m2
1.04
m1
m2
Chisq
R
1.02
1
Value
0.99461
0.23385
15.206
0.97945
Error
0.0019407
0.01232
NA
NA
dashed: n=0.25
solid: n=0.23
0.98
0.96
0.94
6000
7000
8000
9000
10000
11000
2
MOI (oz-in )
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Batting cage study show how bat speed depends
on MOI for college/semipro baseball players
Crisco/Greenwald Batting Cage Study
50
y = m1*(9/m0)^m2
Value
Error
m1
46.218
0.3921
m2
Chisq
0.28747
3.8574
0.057422
NA
R
0.93138
NA
48

knob
46
(rad/s)
44
aluminum
wood
42
40
8.5
9
9.5
10
3
10.5
11
11.5
2
I (10 oz-in )
6"
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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
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More details on the NCAA protocol:
Higher BESR, higher MOI
 same BBS
BESR
same BBS
Same BESR, lower MOI
 Higher BBS
lower BBS
higher BBS
Same MOI, lower BESR
 Lower BBS
MOI
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Example: 34” Bats
BESR
102 mph
0.75
0.73
max vf
BESR limit
97 mph
typical wood
0.71
0.69
MOI limit
0.67
0.65
9000
9500 10000 10500 11000 11500 12000
2
MOI (oz-in )
All bats below horizontal line and to right of
vertical
line
are allowed
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the Performace
of
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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%
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The NCAA bat compliance program has
resulted in return of offensive statistics to
earlier levels
HR
NCAA home runs/game
1.15
1.05
0.95
0.85
0.75
0.65
0.55
0.45
0.35
70 972 974 976 978 980 982 984 986 988 990 992 994 996 998 000 002 004 006
9
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
year
aluminum
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-5 rule
Regulating the Performace of
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BESR MOI
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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
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For slow-pitch softball bats, BPF does not
track with BBS
1.4
Computer simulation
BBS (mph)
101
1.38
100
BPF
1.36
99
1.34
98
BPF
BBS
1.32
97
1.3
96
6500 7000 7500 8000 8500 9000 9500 10000
2
MOI (oz-in )
I do not recommend using a BPF standard for
slow-pitch softballRegulating the Performace of
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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
7/16/2015
Regulating the Performace of
Baseball Bats
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