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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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