What are the rules for communicating with opponents during gameplay, specifically when an opponent attacks a battlefield and asks for a reaction?

Ruling: You must communicate accurately. When an opponent moves to a battlefield and asks if you respond (with no triggers on the chain), they have passed you focus. If you say no, combat immediately resolves and you cannot then play an action spell.

Sequence:

• When a unit moves to battlefield, check if there are any attack/defend/move triggers
• If there's a move trigger, it must be checked for reactions and resolved first
• After the trigger resolves (or if there are no triggers), the attacker gains focus and must pass it
• Once focus is passed to you, you can play actions or pass back
• If you pass, combat resolves

Nuances:

• You can only respond when there's a chain or focus - moving itself creates neither
• To avoid confusion, explicitly state game state changes like "move trigger resolves" instead of just saying "pass"
• When playing against less technical players, verbally clarify the game state (e.g., "move trigger resolves. You have Focus.")