Thomas Francis Hallion (born September 5, 1956) is an American umpire in Major League Baseball (MLB) who has worked in the National League (NL) from 1985 to 1999 and throughout both major leagues since 2005.
He is a crew chief.
Hallion has worn number 20 during his MLB career.
He resigned from the NL in 1999 as a failed mass bargaining strategy, but he was rehired by MLB before the 2005 season.