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 .