I'm defending at a battlefield, my opponent attacks. He passes priority to me, I play a spell. The spell resolves. Who has priority after my spell resolves?

To determine who has priority after your spell resolves during a showdown, we follow the established showdown timing flow.

According to FAQ #9365 and FAQ #5067, in a showdown, when you (the defender) play a spell/reaction and it resolves, priority returns to the attacker.

Sequence of Events:

1. Attacker passes priority: The attacker chooses not to play an action or reaction, passing focus to you.
2. Defender (You) plays a spell: You play a spell to start a chain (or add to one).
3. Chain resolves: The spell executes its effects.
4. Priority returns to the Attacker: Once the chain is empty (or the spell has finished resolving), priority returns to the attacker. They may now choose to play an action, a reaction, or pass priority again.

Important Note: Combat does not resolve until both players pass priority consecutively while the chain is empty. As long as players continue to add items to the chain, the showdown continues. If the attacker passes priority back to you after your spell resolves, and you subsequently pass priority, the showdown will conclude (as per FAQ #8632).