Does the cleanup step use the stack when discarding down to maximum hand size?

During the cleanup step, if the active player has more cards in hand than their maximum hand size (normally seven), they must discard down to that limit. This discard is a rules-based action defined in CR 514.1 and it does not use the stack.

Normally, spells and abilities use the stack, and players receive priority to respond. The cleanup step is a special exception: per CR 514.3, no player receives priority during the cleanup step unless a state-based action is performed or an ability triggers during it. The discard itself simply happens — no one can counter it, respond to it with instants, or otherwise interact before the cards hit the graveyard.

However, if discarding a card causes a triggered ability to trigger (for example, a card with a 'when you discard this card' ability), or if a state-based action needs to be performed, then the cleanup step does enter a mini-loop: players do receive priority in a temporary window, those triggers go on the stack and resolve, and then another cleanup step begins (CR 514.3). But the act of discarding itself still never went on the stack.

Example: You end your turn with eight cards in hand, including Obstinate Baloth. You must discard to seven. Obstinate Baloth does not have a 'when discarded' trigger, so you simply put it in the graveyard. Your opponent cannot cast a Lightning Bolt in response to the discard — no one receives priority during that action.

Key rules: CR 514.1 (cleanup step discard), CR 514.3 (priority only if triggered abilities or SBAs occur), and CR 509.2 for comparison of how the discard phase differs from normal priority windows.