It is a touchback 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 their own goal line and the attacking team is responsible for the ball being there (Rules 7-2-4-c) (A.R. 7-2-4-I, A.R. 8-6-1-I-III).
b. A kick becomes dead by rule behind the defending team’s goal line and the attacking team is responsible for the ball being there (Exception: Rule 8-4-2-b) (A.R. 6-3-4-III).