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Bat Rolling Study
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Broken Bat Guarantee
 A recent Master's Thesis from the Washington State University[1] studied the performance of composite slow-pitch softball bats and the performance improvements gained through various ways a bat might be modidified. The bar chart at right shows test results[1,2] for three bats that were broken-in naturally by hitting balls. Bats JN05 and JE04 are multi-walled composite bats and JA05 is a multi-walled aluminum bat. First, the bats were performance tested brand new, right out of the wrapper, in accordance with the high-speed cannon test (ASTM F2219) used by the ASA to certify bats. Then each bat was used to hit ASA certified 0.44 COR 375lb softballs 500 times in an indoor batting cage. Balls were pitched slow-pitch style, and batters were experience amateurs. After 500 hits the bats were performance tested again. Then another 500 hits and another performance check, and so on until 2000 hits were accumlated.[3]
The results in the bar graph show that all three of the bats showed noticeable improvement of 2.5-3.5 mph in batted-ball speed after the first 500 hits, followed by a slight decrease in performance after 1000 hits. The experimental evidence seems clear - the performance of a bat can improve significantly after the bat has been broken in naturally by using it to hit balls. What does a 3.5mph increase in batted-ball speed mean in terms of performance? The difference between a softball leaving a bat at 98-mph and a softball leaving a bat at 101.5-mph is about 27 feet in distance travelled. That could very easily be the difference between a pop fly to the outfield and a homerun.[3]

This improvement after break-in poses a problem for associations with bat performance standards and certification. All three bats started out meeting the 98-mph criteria (although the JN05 bat was pushing the limit) when tested brand new. However, after 500 hits, all three bats are now above the 98-mph threshold. The ASA requires that a bat pass the certification test at any time during its useful life. So, from the ASA viewpoint, these bats three bats are no longer legal bats after they have been broken in. This is largely why the ASA has moved to begin breaking in bats prior to sending them out for certification testing - and why very few composite bats are able to pass the 98-mph certification performance standard after being broken-in.[3]
[1] Curtis M. Cruz, Characterizing Softball Bat Modifications and Their Resulting Performance Affects, M.S. Thesis in Mechanical Engineering, Washington State University, (2005).
[2] L.V. Smith, C.M. Cruz, A. Nathan and D. Russell, "How Bat Modifications Can Affect Their Response," in Proceedings of the APCST2005
International Congress on Sports Technology, Tokyo Institute of Technology, Tokyo, Japan, (2005)

[3]Physics and Acoustics of Baseball & Softball Bats,Daniel A. Russell, Ph.D.,Graduate Program in Acoustics,The Pennsylvania State University
References
The bar chart at right shows data from a Master's Thesis at Washington State University[1] that investigated the effects of various bat modifications. A collection of composite slow-pitch softball bats were tested using the ASTM F2219 high speed cannon test used to measure batted-ball speed in the laboratory. The bats were then sent away to various bat doctors who used their accelerated break-in techniques on the bats. After being broken in the bats were again tested using the ASTM F2219 98-mph BBS performance test. The bar graph at right compares the before and after results.[3]

Improvement was gained for all techniques, but the BCT process improved the batted-ball speed by 8-9 mph. Recalling that the performance improvement due to natural break-in processes is only about 3 mph, it is difficult to argue that an accelerated break-in process such as BCT is not equivalent to bat doctoring. A process that provides three times the improvement in performance as natural break-in seems to me to be a significant alteration of the bat's performance.

Whether or not ABI techniques are considered as doctoring or not, the advantage gained might disappear in coming years. The ASA currently uses a rolling ABI technique for all new composite bats prior to sending them out for certification testing. Since almost all of the 2007-2008 composite bat models failed to pass the 98-mph certification test after being rolled, I would not be surprised to see some changes in the design of ASA certified composite softball bats for 2009. New bat models will have to be designed so that even after being broken-in they still pass the 98-mph standard. At that point, ABI techniques might not be considered illegal since they would not enable a bat to exceed the required performance limit, but they might enable a player to get their bat to its maximum performance sooner - though at the possible risk of shortening the useful life of the bat.[3]
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