A fault caller is a person responsible for making decisions about the legality of plays in a sport. The linesman is an official who assists the referee in making calls, such as offsides in soccer or out of bounds in basketball. The UMPIRE is the main official who makes the final call on a play. The REF is another term for the UMPIRE. All of these positions are important in ensuring that the rules of the game are followed and that the game is fair.