Definition: The official who lines up on the opposite side of the field from the head linesman. His duties include:
• Assist the head linesman on in making illegal motion, illegal shifts, offside and encroachment calls
• Assist the umpire with illegal use of the hands and holding calls
• Assist the referee on false start calls
• Make sure the quarterback does not cross the line of scrimmage before throwing the ball
• Watch for offensive lineman going downfield too early on punts
• Supervise the timing of the game
• Supervise substitutions by the team on his side of the field
