Definition: The official that lines up 25 yards deep in the defensive backfield on the tight end side of the field. His duties include:
• Keep track of the play clock and call delay of game if it expires
• Make sure the defensive team has no more than 11 players on the field
• Rule on plays that cross the defense's goal line
• Watch all eligible receivers on his side of the field
• Rule on the legality of catches and pass interference penalties on the strong side of the field
• Mark the spot where a play goes out of bounds on his side of the field
• Watch for illegal use of hands by the receivers and defensive backs