Baseball spectating is one of the most popular leisure activities in Asia. Leisure participants with high well-being levels usually demonstrate loyal behavior to the teams they follow. Previous research indicates that professional sport fans are serious leisure participants and their participation has career qualities. The goal of this research was to investigate the relationship of leisure involvement with the well-being of professional sport fans and the possible mediating effect of organizational commitment, a career-related characteristic, on well-being. Some 406 fans of the Brother Elephants Baseball Team in Taiwan were surveyed. The results showed that leisure involvement positively and significantly influenced fans’ well-being and organizational commitment partially mediated the influence of leisure involvement on well-being. This study pioneers the integration of leisure involvement, well-being and organizational commitment in the context of a Professional Baseball League team within Asia. Implications and future research directions are presented.