The NFL requires that the sidelines of its fields be rimmed by a white border six feet wide. This territory is out of bounds, meaning that when a player in possession of the ball allows any part of his body, uniform, or equipment to touch it the play is over and the ball is marked where the player left the field of play and went out of bounds. The area that is in back of the end zone, which is 10 yards deep on both ends of the field, is also out of bounds. This comes into play in instances involving receptions, fumbles and kicks.
When a player goes out of bounds with the football the clock is only stopped during the final two minutes of each half in the NFL. This was not always the case but the rule was implemented to speed up the game. The referee often has to make tough decisions as to whether a player was down legally before making it to the sidelines or if he actually got there before being tackled.
On a legal reception of a pass a receiver must catch the ball and establish both feet in bounds. This leads to many reviews of close plays, with the officials having to decide if the player had possession of the ball and was able to get both feet down. Skilled receivers will make catches and touch one, then the other, foot in the field of play before falling out of bounds with the football. Receptions in the end zone are also subject to these NFL out of bounds rules, with a receiver having to have both feet in and possession before going out either on the sideline or the back of the end zone. If a player is in bounds and goes up to make a reception, a defensive player can knock him out of bounds before he can establish both feet in the field of play, making the catch illegal.
On fumbles that go out of bounds the last team to actually have possession of the football will be awarded the ball. The ball is spotted where it went out of bounds if the offensive team fumbles it out of bounds behind the line of scrimmage. If the ball is fumbled forward and it rolls or is knocked out of bounds it is spotted at the point where it was fumbled. This rule keeps a player from deliberately fumbling a ball forwards and out of bounds to gain yardage. If a team fumbles the ball into and out of the opponent's end zone, it is ruled a touchback once it goes out of bounds. This means that the opponent will be awarded the ball at their own 20 yard line. If a team fumbles the ball out of bounds in the end zone they are defending then a safety is the result, with two points for the other team. This also occurs when a punt is blocked out of bounds in the end zone.
If a kickoff winds up out of bounds without being touched by a member of the receiving team and does not cross the goal line, then the ball is spotted 30 yards from the spot of the kick and belongs to the receiving team. This NFL out of bounds rule discourages kicking the ball out of bounds so that it cannot be returned on a kickoff. This rule does not apply on an onsides kick attempt as long as it is the first try. In that case a five-yard penalty is applied to the kicking team, but they can attempt another kick. If this subsequent kick goes out of bounds before it has traveled 10 yards then the ball belongs to the receiving team. Any kickoff touched by the receiving team before going out of bounds gives the receiving team possession, but at the spot the ball left the field of play.
A receiver cannot go out of bounds and then return to the field of play to make a catch. Players can, however, go out of bounds and return to the field of play to make a legal tackle on a ball carrier. A little known out of bounds rule states that if a player on the receiving team can field a kickoff with even one foot out of bounds then the ball belongs to the receiving team 30 yards from where the ball was kicked.