Is it true that the hammerhead shark doesn't kill a dolphin because a hurd of dolphin can hurt it or kill it?

when a dolphin is alone it can be killed by sharks but when dolphins are moving in packs they can kill the hammerhead shark. A dolphin can poke at a hammerhead shark so that the shark flips into the air. Then the dolphin calls his friends, and they poke the hammerhead to death.