Can you play a reaction spell during your opponent's turn if they don't trigger any chains, and how does Focus work after moving to a battlefield and your opponent responds?

Ruling: You do not get priority during your opponent's turn unless triggers occur or a showdown happens. Focus passes between relevant players until both pass without doing something; after your opponent plays something and the chain resolves, Focus automatically goes back to you.

Sequence:

• Player moves units to battlefield and passes Focus
• Opponent plays action/reaction spell and chain resolves
• Focus automatically returns to the active player
• Players continue passing Focus until both pass without action
• Then proceed to combat damage step

Nuances:

• Reaction spells like Consult the Past cannot be played at the end of an opponent's turn without something creating a chain for it to react to
• You need triggers or showdown to occur during opponent's turn to gain priority