高校野球における先攻と後攻の勝率差の検討

20 年間の夏の甲子園のデータ分析

抄録

In high school baseball games, choosing when to bat influences the likelihood of winning, teams batting second having a significantly higher winning percentage. Three hypotheses can be considered for explaining this trend: the weaker school chooses to bat first (Hypothesis 1), an additional strategy change can favor the team that bats second (Hypothesis 2), and a tied score in a later innings favors the team that bats second (Hypothesis 3). However, to our knowledge, no study has directly tested these hypotheses. Therefore, we analyzed data for all 972 games of the Japan national high school baseball championship tournaments between 1996 and 2015, and the following 5 results were obtained. There was a trend in past Koshien tournaments for weaker schools to bat first when playing against stronger schools (52.8 percent, P = 0.091). The winning percentage for the former was 35.5%, which was significantly lower (P <0.001) than the chance level (50%). In addition, the winning percentage for batting first in games between schools with similar levels of past performance was 44.7%, which was significantly lower (P = 0.025) than the chance level (50%). In games between schools with similar levels of past performance, the winning percentage varied for teams batting first when the bottom half of each inning ended in a tie. In games in which teams were tied at the end of the 6th and 7th innings, the winning percentage of the team batting first was significantly lower (36.0%, P = 0.033; 34.0%, P = 0.016). In other words, Hypothesis 3 was supported, Hypothesis 1 was partially supported, but Hypothesis 2 was not supported. These findings indicate that the higher winning percentage for batting second is attributable to the fact that the weaker school regards itself as inferior to its opponent and therefore chooses to bat first (i.e., the weaker school chooses to bat first) and that the psychological pressure faced when batting first versus batting second differs when there is a tie in the later innings (i.e., a tied score in later innings favors the team that bats second).