A former assistant basketball coach at Stone Child College on the Rocky Boy's Indian Reservation has pleaded not guilty to federal charges alleging he sexually abused a girl, starting when she was 12. Christopher Brown of Box Elder was indicted on charges of sexual exploitation of a child, sexual abuse of a minor, and transportation of child pornography. U.S. Magistrate Judge John T. Johnston presided over Monday's hearing in Great Falls. Brown is detained pending further proceedings. His public defender has declined to comment. Brown was fired from his coaching job shortly after the initial charges were filed in January.