Rule 323.12
9. If the current state is a Neutral Open State and one or more Showdowns are Staged at Battlefields without a Combat staged, the Turn Player chooses one of those Battlefields. A Showdown begins there.
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9. If the current state is a Neutral Open State and one or more Showdowns are Staged at Battlefields without a Combat staged, the Turn Player chooses one of those Battlefields. A Showdown begins there.