Does moving a unit into an uncontrolled/open battlefield (with no enemy units) trigger a Showdown?

Ruling: Yes, moving a unit into any battlefield that you don't control starts a Showdown, even if the battlefield is uncontrolled/open with no enemy units present.

Nuances:

• This allows opponents to play Action cards that specify "use only in your turn or in showdowns" (like Blast of Power) in response to the movement
• This mechanic enables players to attempt to stop opponents from gaining points