Combat will open in one of two ways: when a Combat and Showdown are staged at the same Battlefield and the turn player initiates the Showdown; or when the turn is in a Showdown Open State and a Combat is staged at the Battlefield where the current Showdown is ongoing. See rule 318. Cleanups for more information.
§ 464.1 Core Rules PDF (officieel)
§ 464 Step 1: The Combat Showdown Step
