If there is an ongoing Showdown at the Battlefield where the Combat is staged, that Showdown will become a Combat Showdown and a Combat will be initiated there.
§ 460.1 Core Rules PDF (officieel)
§ 460 A Combat occurs when a Cleanup occurs, there are no items on the Chain, there is a staged Combat at a Battlefield, and no Showdown or Combat is ongoing at any other Battlefield. See rule 318. Cleanups for more information.
