Definition from Wiktionary, the free dictionary
umpire (plural umpires)
- (tennis) The official who presides over a tennis game sat on a high chair.
- (cricket) One of the two white-coated officials who preside over a cricket match.
- (baseball) One of usually 4 officials who preside over a baseball game.
- (American football) The official who stands behind the line on the defensive side.
- The umpire must keep on his toes as the play often occurs around him.
- (Australian rules football) A match official on the ground deciding and enforcing the rules during play. As of 2007 the Australian Football League uses 3, or in the past 2 or just 1. The other officials, the goal umpires and boundary umpires, are normally not called just umpires alone.
- (law) A person who arbitrates between contending parties
Usage notes 
- In general, a referee moves around with the game, while an umpire stays (approximately) in one place.
- (sports, intransitive) To act as an umpire in a game.
- (transitive) To decide as an umpire; to arbitrate; to settle (a dispute, etc.).
- Judges appointed to umpire the matter in contest between them, and to decide where the right lies.
to act as an umpire in a game