Rule 8 – Section 5 – Article 1 – How Scored

It is a safety when:
a. The ball becomes dead out of bounds behind a goal line, except from an incomplete forward pass, or becomes dead in the possession of a player on, above or behind his own goal line, or becomes dead by rule, and the defending team is responsible for the ball being there. (A.R. 6-3-1:IV) (A.R. 7-2-4:I) (A.R. 8-5-1:I-II, IV and VI-X) (A.R. 8-7-2:II) (A.R. 9-4-1:VIII)
When in question, it is a touchback, not a safety.
Exception: It is not a safety if a player between his five-yard line and his goal line:
(a) intercepts a pass or fumble; or recovers an opponent’s fumble or backward pass; or catches or recovers an opponent’s kick; and
(b) his original momentum carries him into his own end zone; and
(c) the ball remains behind his goal line and is declared dead in his team’s possession there. This includes a fumble that goes from the end zone into the field of play and out of bounds (Rule 7-2-4-b-1).
If conditions (a)-(c) are satisfied above, the ball belongs to this player’s team at the spot where he gained possession.
b. An accepted penalty for a foul leaves the ball on or behind the offending team’s goal line. (Exception: Rules 10-2-7-c and 10-2-7-a). (A.R. 8-5-1:III) (A.R. 10-2-2:VI)