What is the first turn-based action after the declare blockers step begins?

The correct response identifies that the defending player declares blockers as the first turn-based action after the declare blockers step begins. In the combat phase, after attackers are declared, the game proceeds to the declare blockers step where the defending player has the opportunity to block the attacking creatures. This action signifies that defenders are made official by the defending player, which leads into the subsequent steps of combat damage resolution.

Understanding the combat sequence is critical in Magic: The Gathering, as each step has specific actions that must occur in a precise order according to the rules. Declaring blockers is the first action that immediately follows the declaration of attackers, as it is during this step that the defending player chooses which creatures, if any, will block the attackers.

The subsequent possible actions, such as assigning damage, drawing a card, or untapping permanents, do not occur until after this initial action of declaring blockers is resolved. Each of these actions occurs in their appropriate phases of gameplay and cannot happen until the step where blockers are declared is fully carried out. This emphasis on the sequence of actions is central to understanding turn-based actions within the game.