When defending at a battlefield that allows bringing a unit back to base when defending, can the attacker use Fox Fire before the defender triggers the battlefield effect to return their unit to base?

Ruling: The battlefield effect triggers first when the showdown starts, before any actions like Fox Fire can be played. The defender can choose to use the battlefield effect to bring a unit back to base before the attacker can play Fox Fire.

Sequence:

• The showdown starts
• The battlefield effect triggers and starts a chain
• The defender chooses whether to use the "can" effect to bring a unit back to base
• After all effects and reactions resolve, actions like Fox Fire can be played
• Once the trigger has passed, the battlefield effect can no longer be used

Nuances:

• Fox Fire is not a reaction unless it's hidden at the battlefield, which it can't be if you are defending that battlefield
• The opponent could react to the chain, but Fox Fire specifically cannot be used as a reaction in this scenario