A referee in baseball who is part of a larger crew that police the game. Umpires initiate and end the game, make decisions and calls on plays, enforce the rules and administer discipline.
Baseball games are officiated by an umpiring crew. Major League baseball games are called by four umpires, one for each base of the diamond. The umpire at home plate is also known as the umpire-in-chief, and is responsible for balls and strikes, fair and foul balls near home plate, and any calls on baserunners in the vicinity. The other umpires are responsible for plays around the bases where they are stationed, with the first and third base umpires responsible for fair and foul balls that cross their respective bases. Each umpiring crew has a crew chief, who is not necessarily the umpire-in-chief, but usually the umpire with the most experience and seniority. The crew chief acts as a supervisor over the other umpires and reports directly to the league office. While any umpire can make a call on any play, responsibility is usually restricted by vicinity. When an umpire is unsure of a call he has made, the crew will sometimes convene and make a final decision after a short discussion.