The professional sports league of Korea start out in the 1980 s with the professional baseball league. Although it has a short history, there are as many as 4 active sports leagues in Korea today, all of which have been established as the most desirable entertainment businesses. The professional sports club needs to secure excellent players through a close competition with other clubs in order to uplift the profitability while professional players aim at the common benefit of enhancing their own values through the prosperity of the sports league they belong to that both parties are in the relationship where they need to cooperate with each other for the greater benefit of the entire sports league. This dynamic relationship of the sports league has a great impact on the sports player contract concluded between the player and the club, which is also involved with a number of legal disputes. This study investigates whether the professional sports clubs take advantage of their superior position to force sports players to sign unfair contract. For this, the legal principles and the reality of sports player contract between the club and the player were examined first along with various contract systems such as draft system, reserve system, trade system, and free agent system. Furthermore, the direction for improvements for the problems revealed in the course of study were suggested in the conclusion.