The main purpose of this legislation is to change the eligibility rules for amateur sports organizations in the United States, specifically regarding the participation of individuals based on their biological sex. The bill aims to ensure that competitions designated for females are exclusively for individuals who are biologically female. Key provisions of the legislation include new definitions for "female," "male," and "sex." It defines "female" as someone with a reproductive system that produces eggs, and "male" as someone with a reproductive system that produces sperm.