When a player contests a battlefield in a showdown, who has priority to play spells/actions first?

Ruling: The player who is attacking/contesting the battlefield gains both focus and priority first at the start of the showdown.

Sequence:

• The attacking player gains focus and priority when the showdown starts
• Focus gives permission to play an action, which starts a chain
• When the attacking player passes priority, they retain focus but the opponent can now add a reaction to the chain
• After the chain completely resolves, the next relevant player gains both priority and focus
• This continues until all relevant players pass

Nuances:

• Focus and priority are different mechanics - focus gives permission to play an action, while priority determines who can add to the chain
• When you pass priority, you retain focus but allow your opponent to respond