Regulating the Performance of Baseball Bats

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

3. 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, … Regulating the Performace of Baseball Bats

4. 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+(BESR+0.5)vbat • vpitch: pitch speed • vbat: bat speed • BESR: Ball Exit Speed Ratio 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 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 Regulating the Performace of Baseball Bats

7. 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 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 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) 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) Regulating the Performace of Baseball Bats

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

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

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

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

16. 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% Regulating the Performace of Baseball Bats

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

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

20. 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 Regulating the Performace of Baseball Bats

21. 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 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 Regulating the Performace of Baseball Bats