411.1. Game Actions may be the responsibility of up to one player. The player that performs the Game Action is responsible for it. Example: Cull the Weak is a spell that reads "Each player kills one of their units." When the spell resolves, each player chooses a unit they control and kills that unit. They are responsible for the death of their own unit.
411.2. In the case where a Game Action is performed by procedures of the game and not by any player, that Game Action is not the responsibility of any player.
411.3. Certain rules assign responsibility to players for Game Actions that they are not normally responsible for.
411.4. If an ability triggers when "you" do something, it triggers when a Game Action that you are responsible for occurs. Example: A gear reads "When you move an enemy unit, you may exhaust this to [Stun] it." It will trigger whenever a move game action that you are responsible for causes an enemy unit to move. If an opponent plays a spell that reads "choose a Battlefield. Each player may move a unit they don't control to that battlefield," and a player that controls the gear chooses to move an enemy unit, their gear will trigger.