[Patriot_Fan2180]

In American football, a touchback is a ruling which is made and signaled by an official when the ball becomes dead on or behind a team's own goal line (i.e., in an end zone) and the opposing team gave the ball the momentum, or impetus, to travel over or across the goal line.[1] Such impetus may be imparted by a kick, pass, fumble, or in certain instances by batting the ball. A touchback is not a play, but a result of events that may occur during a play. A touchback is the opposite of a safety with regard to impetus since a safety is scored when the defending team is responsible for the ball becoming dead on or behind its own goal line.

Examples of instances where a touchback would be awarded include when:
A kickoff or punt enters the end zone and becomes dead behind the goal line without being advanced beyond the goal line by a player of the receiving team. Thus, a player on the receiving team could attempt to advance the ball out of his own end zone, but the original impetus from the kick remains as long as the ball does not completely cross the goal line into the field of play. Note that if a kick is fielded by the receiving team in its end zone, is advanced beyond the goal line, and then the ball carrier retreats back into his own end zone where the ball is downed, it is a safety because the impetus would then be charged to the receiving team.
A kickoff or punt touches the ground in the receiving team's end zone before being touched by a player of the receiving team. However, in American football, the ball is considered live until it is downed by a member of the receiving team. If a kicked-off ball goes untouched into the end zone and then is recovered by a member of the kicking team, it's a touchdown for the kicking team.
A kickoff or punt goes out of bounds behind or over the receiving team's goal line.
A ball carrier fumbles the ball within the field of play forward into his opponents end zone and the loose ball then goes out of bounds behind or above his opponent's goal line or is recovered and downed by an opposing player in the end zone. The opposing team would be awarded the touchback.
A defensive player intercepts a forward pass in his own end zone and the ball becomes dead behind or over the goal line. Like the instance of a kickoff or punt fielded in an end zone, the intercepting player can attempt to advance the ball but it is still a touchback as long as the ball never completely crosses the goal line into the field of play before it is downed.
A blocked punt goes back into the end zone and the defensive team intentionally bats or kicks the ball out the back of the end zone. Offense must decline penalty.