cr:7.3.2f

If there are two or more attack-targets, defending cards are declared for each attack-target in clockwise order of their controller, starting from attacking hero.[1.1.6] Then, if two or more attack-targets are controlled by the same player, defending cards are declared for each attack-target in an order determined by that controlling player. Cards only defend the attack-target they are declared for. All declared cards for each attack target are put onto the active chain link in separate events as defending cards.

Example: Apocalypse Automaton has the text “This attacks up to X target opposing heroes, . . . .” If two players’ heroes are attacked by an Apocalypse Automaton, the defending cards for each hero are declared in clockwise order from the controller of the attack. The first hero’s player declares defending cards, then any player may declare additional defending cards (such as cards with Protect), and finally, those declared cards become defending cards for that hero. This process then repeats for the second hero.