In a multiplayer game, can you choose to attack a planeswalker controlled by a player you are not attacking?

When you attack in a multiplayer game, you first choose a single defending player (or, in some formats, a planeswalker or battle as the defending entity). Each attacking creature must be declared as attacking either that defending player or a planeswalker or battle controlled by that defending player. You cannot split your attack so that creatures go to planeswalkers owned by different players unless those players are all chosen as defending players under the applicable multiplayer rules.

CR 506.2 states that during the declare attackers step, the active player declares each creature they control as either attacking a player or attacking a planeswalker or battle. CR 508.1 further clarifies that each attacking creature must be assigned to attack a single player, planeswalker, or battle. In a Free-for-All multiplayer game (CR 806), you may choose multiple defending players only if the format rules allow it — but each creature still attacks a specific player or a permanent controlled by that player.

In typical multiplayer (Free-for-All), you choose one defending player per attacking creature, and any planeswalker you redirect that creature to must be controlled by the same player that creature is attacking. You cannot have Creature A attack Player B while simultaneously assigning it to a planeswalker controlled by Player C.

Example: You control two creatures. Player B controls a planeswalker; Player C also controls a planeswalker. You may attack Player B and assign one creature to their planeswalker, and attack Player C with the other creature and assign it to Player C's planeswalker — but you cannot have a single creature attack Player B while targeting Player C's planeswalker.

This is governed by CR 506.2 and CR 508.1, which together require that each attacker's target (player, planeswalker, or battle) be consistent — a planeswalker can only be attacked by a creature that is attacking the player who controls it.