Historical Rules · 13 October 2023
Rule 704.5w
Official source text from the 13 October 2023 Rules release
If a battle has no player in the game designated as its protector and no attacking creatures are currently attacking that battle, that battle’s controller chooses an appropriate player to be its protector based on its battle type. If no player can be chosen this way, the battle is put into its owner’s graveyard. See rule 310, “Battles.”