Does moving a unit to a battlefield you already control cause a showdown?

Ruling: Moving a unit to a battlefield you already control does not cause a showdown.

Sequence:

• If you control a battlefield with a unit and move another unit there, no showdown occurs
• If you leave a battlefield (making it unoccupied) and then move back in with a different unit, a showdown does occur

Nuances:

• The opponent does not get priority when you move a unit from base to a battlefield you control, unless the moving unit has a move trigger (like Merchant)
• Shen can only be played to a battlefield you control, so it cannot be used to react to an opponent moving to their own controlled battlefield