When is the damage assignment order chosen if an attacker is blocked?

The damage assignment order is chosen during the declare blockers step. This step occurs after attackers have been declared and before damage is dealt. During this time, the defending player has the opportunity to declare blockers, which is crucial because it determines how combat damage will be assigned if the attacking creature is blocked.

During the declare blockers step, the defending player can choose to assign damage in a specific order if the blocked creature has multiple blockers. This order can influence how damage is assigned and how creatures may be affected based on their toughness or any damage dealt to them.

The other options do not represent the correct moment for choosing the damage assignment order. The beginning of combat step is prior to declaring attackers, where players do not have information about blockers yet. The declare attackers step is when the attacking player declares which creatures are attacking, but again, the damage assignment order is not relevant at that point. Finally, the combat damage step is when damage is actually dealt; by this time, the order must have already been established in the declare blockers step. Thus, it is specifically during the declare blockers step that players choose how damage will be assigned.