Does Green Yasuo's 'when I attack' ability trigger when he is swapped onto a battlefield using Tideturner while defending (opponent is attacking)?

Ruling: Green Yasuo's ability does not trigger in this scenario. The attacker/defender designation is determined by who initiated the contested status on the battlefield, not by which units move onto it. Since the opponent is attacking the battlefield, Yasuo is a defender and does not gain the attacker designation.

Nuances:

• The player who initiates contested status on a battlefield is the attacker, regardless of which units move onto the battlefield
• 'When I attack' abilities trigger the first time a unit gains the attacker designation in each combat
• A unit can gain the attacker designation multiple times in a single combat, but the 'when I attack' ability only triggers the first time per combat
• A unit can trigger 'when I attack' abilities multiple times per turn if it participates in multiple combats