What triggers a showdown in Riftbound?

Ruling: A showdown is initiated when one of your units moves to a battlefield you do not control. If there is an opponent present, it's a combat showdown; otherwise, it's an open showdown.

Sequence:

• Your unit moves to a battlefield you do not control
• Showdown is initiated
• If opponent units are present: combat showdown
• If no opponent units are present: open showdown

Nuances:

• Moving to an empty field (that you don't control) does trigger a showdown, specifically an open showdown