I heard someone mention a "third team" in a football game. What is that? Who are these guys and what do they do?

A football game actually consists of three teams, with the third team being the officiating crew. They also have a uniform, which consists of a shirt with vertical black and white stripes, white pants, and a white or black hat. These men are responsible for enforcing the rules of the game as outlined by the NFL rules committee. An NFL officiating crew consists of six men, and each has distinct responsibilities:

Referee - This is the head official on the field. He is responsible for giving signals and serves as the final authority on rule interpretation. If you watch an NFL game, this will be the official making announcements.
Umpire - The umpire rules on players' equipment and conduct. The umpire takes a position about five yards behind the line of scrimmage.
Head Linesman - The head linesman is responsible for calling infractions of player movement when lined up on the line of scrimmage. He also keeps track of the downs and manages the chain crew.
Line Judge - The line judge keeps time during the game to backup the official clock operator. Also, he backs up the head linesman on line-of-scrimmage calls. He straddles line of scrimmage on the opposite side from the Head Linesman.
Field Judge - The field judge makes calls regarding the wide receivers and backs on his side of the field. He also watches the defensive players that the back is blocking. He makes calls determining if a player is in or out of bounds. He stands 20 yards away from the line of scrimmage at the beginning of a play, on the same side of the field as the Line Judge.
Side Judge - The side judge makes calls regarding the wide receivers and backs on his side of the field. He also watches the defensive players the back is blocking. He makes calls determining if a player is in or out of bounds. He stands 20 yards away from the line of scrimmage at the beginning of the play, on the same side of the field as the Head Linesman.
Back Judge - The back judge makes calls regarding the tight end and the player the tight end might be blocking. He is also responsible for keeping the time for the 25-second play clock, time outs, and intermissions. He stands 25 yards beyond the line of scrimmage.

These men must memorize and be ready to call an infraction in a split second. An official signals an infraction by throwing a yellow flag. There are many rules in the NFL Rule Book; here are a few of the ones of which you might be unaware:

Clipping - This is a block thrown in the back of the opposing player.
Chop block - This is an illegal block thrown below the waist of an opposing player. These types of blocks have been known to cause severe leg injuries to the opposing player. The offensive team is penalized 15 yards for this infraction.
Encroachment - A defending player moves into the neutral zone and makes contact with an offensive player before the ball is put in play. The neutral zone is a space the length of the ball that separates the offense and defense prior to a play. The only player who can legally enter the neutral zone is the center, who hands, or snaps, the ball to the quarterback to start a play. The offensive team is awarded 5 yards for this penalty.
Excessive crowd noise - The referee determines that the crowd is too loud. The home team can be penalized 5 yards or can lose a time out.
Fair catch - A player receiving a kick or punt can signal that he does not intend to return the ball by putting his arm in the air. Once he signals for a fair catch, he cannot be tackled and cannot move beyond the spot where he catches the ball.
Intentional grounding - A quarterback, who is in the pocket, intentionally throws the ball away to avoid being tackled behind the line of scrimmage for a loss of yards. The pocket is the rounded shape formed by the offensive linemen during a play when they are blocking for the quarterback.
Leaping rule - While players can block kicks, they cannot run from more than 1 yard behind the line of scrimmage to do so. According to NFL rules, a defensive player can run forward and leap in attempt to block a kick if he was lined up within 1 yard of the line of scrimmage when the ball was snapped. But if the player is lined up more than 1 yard from the line of scrimmage, he can not run up to the line, leap to block a kick and land on other players. A 15-yard penalty is assessed for this infraction.
Tuck rule - A player, typically the quarterback, drops the ball when his arm is moving forward to tuck the ball away. The action is considered an incomplete pass rather than a fumble because his arm is moving forward.
"Emmitt Smith" helmet rule - A player cannot remove his helmet on the field unless it is to adjust his equipment. This rule is dubbed the "Emmitt Smith rule" because Smith, who holds the record for most rushing touchdowns, was famous for ripping off his helmet to celebrate a touchdown. This rule was enacted to quell excessive celebrations. The team of the offending player is assessed a 15-yard penalty.

For more information about American football, check out How American Football Works.

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