At the end of any down, the referee can request the head linesman and his assistants to bring the yardage chains onto the field to determine whether the ball has reached the necessary line for a new first down. The referee also notifies the head coach when any player is disqualified for unnecessary roughness or unsportsmanlike conduct and tells the coach on whom each penalty is called.
Umpire The umpire is responsible for the legality of the players’ equipment and for watching all play along the line of scrimmage, the division line between the offensive and defensive players. He makes sure that the offensive team has no more than 11 players on the field prior to the snap of the ball. At the start of a play, he positions himself 4 to 5 yards off the line of scrimmage on the defensive side of the ball. Consequently, if he’ s not quick on his feet, the umpire is the official most likely to be trampled by oncoming players, especially ball carriers running up the middle. Because he’ s responsible for monitoring the legality of all contact between the offensive and defensive linemen, this official calls most of the holding penalties. He also assists the referee on decisions involving possession of the ball in close proximity to the line of scrimmage. He records all timeouts, the winner of the coin toss, and all scores, and he makes sure that the offensive linemen don’ t move downfield illegally on pass plays. Finally, when it’ s raining, the umpire dries the wet ball prior to the snap.
Head linesman The head linesman sets up on the side of the field designated by the referee. He straddles the line of scrimmage and watches for encroachment, offside, illegal men downfield, and all the other line-of-scrimmage violations. He’ s also responsible for ruling on all out of bounds plays to his side of the field. The linesman is responsible for the chain crew and grabs the chain when measuring for a first down. He’ s usually the official who runs in after a play is whistled dead and places his foot to show where forward progress was made by the ball carrier at the end of the play.