When a unit is moved to a battlefield, does contested status apply immediately during movement-triggered abilities? And if Player A controls a battlefield with one unit, Player B plays a spell to move that unit off, and Player A reacts by moving Player B's unit onto that battlefield, does Player A retain control since the battlefield becomes contested?

Ruling: Contested status is gained immediately when a unit moves to a battlefield, so the battlefield is contested during abilities triggered by the unit moving. In the scenario where Player A reacts to prevent losing control, Player A would hold the battlefield until combat is resolved, though there are some edge cases about whether this creates a combat situation that need clarification.

Sequence:

• Player B plays spell to move Player A's unit off the battlefield
• Player A reacts with spell to move Player B's unit to that battlefield
• Player B passes, Player A passes
• Player B's unit moves onto the battlefield, triggering a staged showdown
• Priority passes, Player B passes, Player A passes
• Player A's unit is moved to base
• Chain is empty and showdown begins with Player B applying contested status to the battlefield which is still under Player A's control

Nuances:

• There is debate about whether this creates a combat or just a showdown, since when the chain resolves there may not be units from both players present
• The rules around control lock during contested status have not been fully ironed out
• The recommended approach is to treat it as a combat to avoid breaking the game