Alrighty. I'll go by what Cryuel says, but I found what the smogon rules are.
It's the rocky helmet clause sorta on smogon.
If induced recoil from an ability (Rough Skin/Iron Barbs/Liquid Ooze/Aftermath, Rocky Helmet) results in a double faint, the winner is the Pokemon with the ability that caused the recoil faint. This means that if you punch a Ferrothorn and Iron Barbs causes a double KO, the Ferro wins