彈力球實戰──棒球恢復係數對職業棒球打者打擊表現及策略的影響

The Juiced Ball Effect: The Impact of Baseball Coefficient of Restitution on Batting Performance and Strategy in Professional Baseball

緒論：為調整投打平衡，中華職棒於2020至2021年使用了高、中、低三種不同恢復係數（coefficient of restitution, COR）的球。高COR的棒球俗稱為彈力球，一般認為棒球的恢復係數會影響打擊表現，然而並無實際於比賽中收集的數據佐證。方法：本研究通過TrackMan系統收集了中華職棒2020年上半球季（高COR球）、2020年下半球季（中COR球）和2021年上半球季（低COR球）共128名打者的打擊成績，比較三個球季間打者的打擊率、長打率、每安打平均打席數、每全壘打平均打席數、每四壞球保送平均打席數、每三振平均打席數，同時分別探討三個半季間打者擊出飛球、平飛球與滾地球時的擊球速度、飛行角度、旋轉轉速以及飛行距離等擊球表現，探討棒球恢復係數與擊球表現的相關。結果：比賽用球的COR越高，打者擊成高飛球的擊球速度越高，飛行距離最遠，而擊成滾地球的擊球速度也會最高。而當彈性降低時，為彌補球的彈性的不足，打者會刻意加大擊球角度與擊球轉速，然而數據顯示此為錯誤策略，應以增加平飛球擊球機率為較佳策略。結論：比賽用球的COR會影響打者的進攻表現，也可以透過改變用球的COR來調整聯盟之中的投打平衡。比賽的外在因素如比賽用球改變時，選手和教練不應僅依靠直覺，而是應該參考大數據分析調整自身比賽策略，方為上策。

Introduction: To adjust the balance between pitching and batting, the Chinese Professional Baseball League (CPBL) used three types of baseballs with different Coefficients of Restitution (COR) - high, medium, and low - between 2020 and 2021 seasons. The baseball with a high COR is commonly known as a ''juiced ball.'' It is generally believed that the COR of a baseball affects batting performance; however, no actual game data had been collected to support this claim. Methods: The TrackMan system was used to collect the batting performance data from 128 players in the CPBL using during the first half of the 2020 season (high COR ball), the second half of the 2020 season (medium COR ball), and the first half of the 2021 season (low COR ball). Batting statistics compared across the three seasons included batting average, slugging percentage, plate appearances per hit, plate appearances per home run, plate appearances per walk, and plate appearances per strikeout. Additionally, the batted ball performance—such as exit velocity, launch angle, spin rate, and flight distance of fly balls, line drives, and ground balls—was analyzed across the three half-seasons to explore the correlation between the COR and batting performance. Results: The higher the COR of the baseball, the higher the exit velocity and flight distance for fly balls, as well as the higher exit velocity for ground balls. As the ball's elasticity decreased, hitters tended to increase launch angle and spin rate to compensate for the reduced elasticity. However, data suggest this is an incorrect strategy, and increasing the frequency of line drives would be a better approach. Conclusion: The COR of the baseball used in games affects batting performance and can be adjusted to balance pitching and hitting within the league. When external factors, such as changes in game balls, occur, players and coaches should not rely solely on intuition but instead use data analytics to adjust their strategies for optimal performance.