The jurisprudence of antitrust law has profound impacts on labor practices and structures of professional sport leagues in the United States and other parts of the world. While American antitrust law has been benchmarked by a number of countries including South Korea, the legal notions developed by U.S. court system in regards to spectating sport industry were not adopted in other foreign jurisdictions. This chapter introduces fundamental rules of American antitrust jurisprudence in the context of the major professional sports, particularly focusing on the labor relationship between players unions and sport leagues. Secondly, it explains Korean competition law that benchmarked the U.S. counterpart in order to regulate monopoly and unfair competition in the country. It explores several antitrust implications involved with the Korean Baseball Organization (“KBO” hereafter), which is equivalent to the Major League Baseball (“MLB” hereafter) in the U.S. Given the comparative exploration of the regulations, the paper concludes that some antitrust challenge or administrative enforcement against the KBO is conceivable.