Forty years ago, US president Richard Nixon signed Title IX into law, making it illegal for federally funded education programs to discriminate based on sex. The law set into motion a massive boom in girls and women’s sports teams, from kindergarten to the collegiate level. Professional women’s sports grew in turn. Title IX became a massive touchstone in the fight for gender equality. So why do girls and women-including trans and intersex women-continue to face sexist attitudes and unfair rules and regulations in sports?