Does Yasuo's 'When I attack, deal my might as damage to a unit' ability trigger and resolve before combat damage in a showdown, and can it kill the defending unit before combat occurs?

Ruling: When a showdown is initiated, triggered abilities go on the chain starting with the attacker's "When I attack" triggers, then the defender's "When I defend" triggers. After reactions are played and the chain resolves, combat occurs. A unit killed by Yasuo's ability during the initial chain will not be present for combat and does not contribute damage.

Sequence:

• Attacking player activates their "When I attack" triggers in their desired order
• Defending player activates their "When I defend" triggers in their desired order
• Players can activate reactions in sequence, passing priority back and forth
• After each item on the chain resolves, a cleanup occurs
• After the initial chain fully resolves, the attacking player gains focus to play Action spells
• Players alternate playing actions until both pass
• Combat damage calculation is performed

Nuances:

• If a defending unit survives Yasuo's damage due to a "When I defend" ability or reaction that increases its might, it remains in combat with damage on it
• If you were unable to react to Yasuo's trigger and your unit was defeated by it, it will not be there for combat
• You can activate reactions during the initial chain, which will resolve before attack and defend abilities
• Even if all defending units are removed, players can still play actions before combat would occur