"The goal line is the chalked or painted line dividing the end zone from the field of play in American football and Canadian football. It is the line that must be crossed in order to score a touchdown
If any part of the ball reaches any part of the imaginary vertical plane transected by this line while in-bounds and in possession of a player whose team is striving toward that end of the field, this is considered a touchdown and scores six points for the team whose player has advanced the ball to, or recovered the ball in, this position. This is in contrast with other sports like Association football and ice hockey, which require the puck or ball to pass completely over the goal line to count as a score.
If any member of the offensive team is downed while in possession of the ball behind his own team's goal line, this is called a safety and scores two points for the defensive team.
If, during the course of play, a loose ball travels past the goal line and is recovered within the end zone, then it is a touchdown if recovered by the kicking team, or a touchback if recovered and downed by the receiving team.
In the event of a kick recovered in one's own end zone, the entirety of the ball must pass the goal line in order for the ball to be considered in the field of play, and not a touchback." [Goal line (gridiron football). Wikipedia]
The American football positions diagram example "Goal line formation (Offense/Defense)" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Football solution from the Sport area of ConceptDraw Solution Park.