Definition: The head linesman is the official that sets up straddling the line of scrimmage on the sideline designated by the referee. His duties include:
• Watch for line of scrimmage violations like offsides and encroachment
• Rule on all out-of-bounds plays on his side of the field
• Keep tabs on the chain crew
• Mark the chain to a yard marker on the field as a reference point for a measurement on the field
• Mark a players forward progress after a play is whistled dead
• Keep track of all eligible receivers
• Watch for illegal motion, illegal shifts, illegal use of hands, illegal men downfield