When does a player gain control of a battlefield when moving a unit to an uncontrolled battlefield - immediately upon arrival outside of combat, or after the showdown resolves?

Ruling: A player cannot gain control of a contested battlefield immediately upon moving a unit there. Moving a unit to a battlefield you don't control makes it contested, and you must go through the showdown process until the end and still be the only player who controls a unit there in order to gain control of it.

Sequence:

• Unit moves to uncontrolled battlefield
• Battlefield becomes contested
• Showdown occurs at end of move's cleanup
• All players pass focus in a row
• Final showdown procedures occur
• If you are the only player with units there at the end, you gain control

Nuances:

• For unoccupied battlefields specifically, the showdown final procedures are detailed in rule 345.2
• Rule 181.4.a describes the general state of control but not the precise mechanism by which control is gained