In generation three games, like sapphire, ruby, emerald, fire red, and leaf green, Crunch is a special move. In generation 1-3, a move being physical or special is based solely on it's type. Like shadow ball was physical because it was a ghost type. Crunch is physical in generation 4 because They changed it to be based on the attack itself.
So
gen 3-special
gen 4-physical