| Summary: | 碩士 === 國立臺灣體育運動大學 === 運動管理學系碩士班 === 100 === The prediction of performance for professional baseball players is required in determining the length and the amount of contracts and trades. The method which teams generally use at present is based on the player’s performance in previous years. Therefore, a more reliable method is required to predict the future performance of the players. There are several studies investigating the performance changes with age in Major League Baseball. There is no study examining the aging effect in performance in Nippon Professional Baseball. The baseball players in Japan and Taiwan have similar body type and genetic background. Therefore, the results from, Nippon Professional Baseball could be used as a reference for Chinese Professional Baseball League. The purpose of this research is to analyze the trend of career performance changes with age in Nippon Professional Baseball. This study used four adjusted statistics: batting average, isolated power, triples percentage, and doubles plus triples percentage, and unadjusted base on balls percentage as the indicators for performance. The subjects included Nippon Professional Baseball hitters who have played at least eight years and had 200 or more plate appearances in each year. In order to compare the hitters from different era, this study normalized the yearly numbers to the league average of that category in the specific year. The results showed that the highest batting average occurred between 26 to 29 years old; the highest base on balls percentage occurred in 31 years old; the best isolated power occurred between 26 to 28 years old; the highest triples percentage occurred between 26 to 27 years old; and highest doubles plus triples percentage occurred between 26 to 28 years old. The hitters with high batting average also showed good isolated power, triples percentage and doubles plus triples percentage. The players with good base on balls percentage also showed high batting average, isolated power and doubles plus triples percentage. The hitters with good isolated power also showed high batting average, base on balls percentage, and doubles plus triples percentage. The hitter with high triples percentage also showed high batting average and doubles plus triples percentage. The players with high doubles plus triples percentage showed higher performance in all other categories. The hitters with high performance in two categories were also good at other categories. The results of this study could provide a more objective prediction of aging effect in hitting performance in Nippon Professional Baseball. These information can be used in contract negotiations and served as the reference for the development of professional baseball in Taiwan.
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