308. At any given time, the turn is in either a Neutral State or a Showdown State.

308.1. If a Showdown is in progress, the turn is in a Showdown State.

308.1.a. Only cards and abilities with the Action or Reaction keywords can be played or activated in a Showdown State.

308.2. If no Showdown is in progress, the turn is in a Neutral State.