In a 4-player game, if Player A moves to an empty battlefield starting a showdown, Player B uses Ride the Wind to join, then Player B uses Fight or Flight to remove Player A's unit, can Player A use Ride the Wind to move back to that battlefield?

Ruling: No, Player A cannot move back to the battlefield. Once combat is staged between two players, rule 436.1 prevents units controlled by players who don't already have permanents at that battlefield from moving there, even if one of the original combatants has no units remaining.

Sequence:

• Player A moves to empty battlefield, starting a showdown
• Player B uses Ride the Wind to move a unit there (becomes defender)
• Combat is now staged between Player A (attacker) and Player B (defender)
• Player B uses Fight or Flight to remove Player A's unit
• Player A cannot Ride the Wind back because they no longer have permanents at the battlefield and combat is still in progress

Nuances:

• Rule 423.2 prevents units from moving to a battlefield that already has units from 2 other players present
• Rule 421.2.b causes units to recall if they try to move to a battlefield where a combat is happening between two other players
• Rule 436.1 prevents moves to battlefields with staged combats or combats in progress by players who don't already have permanents there
• There appears to be a rules gap if the original attacker's unit is removed before combat resolves, as the attacker designation remains but they have no units present