Abstract: The theoretical foundation of sports law lies in sports rules, which should serve as the core category in constructing the knowledge system of sports law. Through the four standard examinations of foundationality, distinctiveness, generativity and irreducibility, sports rules satisfy all the conditions required of a core category. Sports rules consist of constitutive rules and safeguarding rules, possessing the dual nature of conventionality (voluntarily accepted by participants) and disciplinarity (embodying the values of the civilizing process). At the ontological level, sports rules constitute the logical starting point of sports law; at the methodological level, the relationship between sports rules and state laws constitutes the basic framework for analyzing the phenomena of sports law. And at the level of content system, the research content of sports law can be categorized into five types: sports autonomy, normative spillover, normative concurrence, industrial extension, and state guarantee, forming a continuous spectrum from "rules completely constituting" to "law directly regulating" within the analytical framework. Sports law, therefore, is an independent legal discipline that takes the operation of sports rules and their relationship with state laws as its research object, rather than a mere application field of traditional branches of law.