The End Zone
A touchdown is the most desirable result for a team in all of American football, because it yields the most points. In order to score a touchdown, a player with the ball must reach the end zone, which is a 30-foot-deep stretch of grass at each end of the football field. According to the official NFL rulebook, the ball must enter the end zone, not simply the player. If a player with the ball steps into the end zone but is tackled before he can get the ball into it, a touchdown is not awarded.
The plane is a metaphorical wall separating the end zone from the rest of the field and must be broken by the ball in order for a team to be awarded a touchdown. There is a thick white line along the bottom of the plane known as the goal line. In order for a touchdown to be scored, the ball must cross this line and be in complete possession, known as "breaking the plane." If even the tip of the ball breaks the plane, a touchdown is awarded as long as the player with the ball has full control of it. If a player is juggling a ball and drops it as he goes into the end zone or if a player goes out of bounds in the back of the end zone and referees deem he did not have complete control of the ball, a touchdown is not awarded.
The Around-the-World Rule
If a player's body is out of the field of play, but he has not touched the ground (for example, if they are leaping and are airborne), has complete control of the ball and stretches the ball back into the field of play, then the plane is considered to go "around the world," meaning that the plane is infinitely wide until the player touches the ground. For example, if a player is heading toward a corner of the end zone, which is marked by an orange object known as a pylon, and leaps into the air, even if he lands out of bounds, a touchdown is awarded if he manages to get the ball to break the plane before hitting the ground. His body's position, in this case, does not matter as long as he does not touch the ground before the ball breaks the plane.