Is The Baseball Juiced Alan M Nathan anathanillinois

Is The Baseball Juiced? Alan M. Nathan a-nathan@illinois. edu @pobguy baseball. physics. illinois. edu 1

Is The Baseball Juiced? 1. Why the current interest? 2. What does “juicing” mean? 3. What do the data tell us? 4. Summary/conclusions 2

1. Why the current interest? Boston Herald ESPN 3

1. Why the current interest? (see The Hardball Times, 7/18/16) 24% increase in HR…. WHY? ? ? 4

2. What does “juicing” mean? Coefficient of Restitution • 5

MLB Specifications • Fire ball from air cannon at 58 mph onto ash board • COR has to fall in the range 0. 514 -0. 578 6

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Data From Sports Science Laboratory, WSU • MLB “spec” is “yuge” 3 balls tested – 11% spread at 58 mph – Extrapolates to ~6. 5 mph spread in exit speed for typical MLB impacts (~160 mph) • Test speed matters! – Balls that perform identically at low speed do not necessarily do so at high speed 8

Higher speed more sensitive to interior of ball 9

Data from Sports Science Laboratory, WSU 2004 baseballs more tig bunched than 1970’s baseballs Error bar ~0. 003 (~0. 4 mph exit speed) 10

Effect of COR on Exit Speed (a brief technical aside) • 11

MLB Ball Testing • Done by Baseball Research Center at UMass/Lowell • Nothing known publicly – Sample size? – Impact speed? – # impacts/ball – Allowable limits on mean, variance? – Year-to-year variation 12

This was big issue in 2000 13

Deep Dive into Recent Data 14

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• A 1. 5 mph increase in exit speed accounts for most of increase in HR • Is this evidence for juiced ball? Change in COR by 0. 012 16

50 buckets 17

250 -300 00 -100 18

Some Remarks • The exit speed data for typical HR launch angles are consistent with increase in COR • The exit speed for line drives are not – “If it doesn’t fit, you must acquit. ” • We have a definite puzzle • Perhaps Brian Mills will solve it in the next talk 19