This is one of the referees who controls the game. The field judge will line up 25 yards deep in the defensive backfield, and his responsibilities include watching the game clock and watching for pass interference penalties, illegal use of hands by defensive players, proper count of players on the field, and the spot where a player goes out of bounds on his side of the field.
This referee is in a very difficult spot on the football field. In a game between the Saints and Panthers, referee Phil Luckett was in the way of a wide open Joe Horn, who was about to catch a touchdown pass. The ball hit Luckett in the head and bounced to the turf.