When combat starts, is there a window to play cards before Attack/Defend abilities trigger, and does Teemo, Strategist's errata prevent him from triggering his Defend ability when played from hidden during combat?

Ruling: There is no window to play cards between starting combat and when Attack/Defend abilities trigger, unless a triggered ability occurs during movement that creates a priority window. Teemo, Strategist still works when played from hidden at reaction speed during combat because "When I Defend" triggers when a card gains the defending designation, not only at the start of combat.

Sequence:

• Combat starts and Attack/Defend abilities trigger immediately
• Players get priority to respond after these triggers are on the chain
• If Teemo is played from hidden at reaction speed during the showdown, he becomes a defending card
• When he gains the defending card designation, his "When I Defend" ability triggers

Nuances:

• The only exception for a window before Attack/Defend triggers would be if a triggered ability occurred during movement (such as a merchant move trigger)
• Teemo's errata was specifically implemented because of changes to defender triggers, to ensure he doesn't trigger twice