Can Player A play an Action (Cleave) after Player B plays a Reaction (Smoke Screen) in response to Player A's attack during a showdown?

Ruling: No, Player A cannot play Cleave immediately after Player B plays Smoke Screen. Player A can only play Reactions while Player B still has Focus and the chain exists.

Sequence:

• Player A attacks and passes priority (also passing Focus since chain is empty)
• Player B plays Smoke Screen (Reaction) and now has Focus
• Player A can only play Reactions at this point, not Actions
• If both players pass priority in succession, Smoke Screen resolves
• After Smoke Screen resolves as the last item on the chain, Priority and Focus automatically pass to Player A
• Player A can now play an Action like Cleave since the chain is empty
• The showdown only moves to damage step once both players pass Focus in a row without doing anything

Nuances:

• Actions can only be played while the chain is empty
• When passing priority while the chain is empty, you also pass Focus
• Priority passes automatically only when a chain item resolves
• A player can play multiple cards during their own priority before passing