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The Rocky Helmet glitch occurs in Pokémon Sun and Moon.
In Battle Spot games, if two players' last remaining Pokémon are knocked out in Battle Spot due to a physical move and the recoil damage from Rocky Helmet, then due to an error the Pokémon that was holding the Rocky Helmet will be determined the winner.
It was intended that the other Pokémon (which dealt the attack and fainted due to the recoil damage) would be regarded as the winner.