The defending card is the closest card on the defending team directly opposite the attacking card with possession.
If the defender has just one card directly opposite the attacking card, that is the defending card - it doesn’t matter whether they are in the front or back line.
If the defender has cards in both the front line and the back line, opposite the attacking card, the front line card becomes the defending card.
If the defender has no cards in either the front or back line, opposite the attacking card, there is no defending card and the attack automatically succeeds.
If the defender has just one card directly opposite the attacking card, that is the defending card - it doesn’t matter whether they are in the front or back line.
If the defender has cards in both the front line and the back line, opposite the attacking card, the front line card becomes the defending card.
If the defender has no cards in either the front or back line, opposite the attacking card, there is no defending card and the attack automatically succeeds.