Rule 8 – Section 5 – Article 1 – How Scored

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.

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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.

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.

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American Football Rules IFAF Approved Ruling 8-5-1:I

I. A10, after receiving the snap in his own end zone, is downed with the ball resting on his goal line, its forward point being in the field of play. RULING: Safety. A part of the dead ball is on the ball carrier’s goal line. [Cited by 2-9-2, 4-2-4-a, 5-1-3-a-1, 8-5-1-a]