To determine whether loss aversion, an important concept in prospect theory, is influential in Japanese baseball, this study conducted a case study of a baseball head coach. The purpose of this study was to elucidate (1) whether or not loss aversion influences decision-making among Japanese baseball head coaches, and (2) if loss aversion does influence decision-making, to determine how these practices were implemented. The following findings were obtained.

　1) One of the head baseball coaches for a Japanese college team consistently exhibited loss aversion. This type of decision-making was referred to as “loss-averse decision-making” in this study.

　2) The loss-averse decision-making was the result of a process in which the head coach of a college baseball team felt tension and lack of power, and placed an excessive emphasis on short-term outcomes.

　3) The college baseball head coach overcame loss-averse decision-making in this case study by using a league championship as a reference point. The change in reference point occurred when the coach perceived a change in the external environment, including suggestions from the mentor.

　4) Loss-averse decision-making was overcome when the head coach of the college baseball team reflected on his coaching by observing the head coach of the opposing team, thereby increasing his pitching options.