When I move to an open battlefield and an opponent uses Zenith Blade to join that battlefield, who is the attacker and who is the defender?

Ruling: The player who moved to the open battlefield first is the attacker. The player who used Zenith Blade to join afterward becomes the defender.

Sequence:

• First player moves to open battlefield, applying contested status during noncombat showdown
• Second player uses Zenith Blade to join the battlefield
• When staged combat begins, the first player is automatically the attacker and the second player becomes the defender

Nuances:

• This is notable for Zenith Blade because if the battle ends in a tie due to stuns, the attacking units that are still alive will be recalled to base, allowing the Leona player to gain control of the battlefield and score a point