This paper examines the determinants of wins in Japan's National High School Baseball Championship (Summer Koshien) by focusing on the role of player origin diversity. Using team information and performance statistics for the period 2014-2015, empirical results obtained using a count data model show that a power pitcher and team batting average are two core offensive and defensive performance statistics on determining the winning game number. Teams with greater experience in this tournament are likely to win more games in this two-week high-pressure tournament. By recruiting players from other prefectures, player diversity exhibits a significantly positive relationship with number of wins. The HHI index (0-1) of player origin diversity increases 0.1 accompanies with more 0.246 game of wins. The specific draw scheme of Summer Koshien does not matter to number of wins, though some teams need one fewer win on the way toward being a champion.