Why are sharks afraid of dolphins?

Dolphins are highly intelligent, social predators. A pod can consist of about a dozen individuals, more if food is plenty. Individuals in the pod help each other out, to the point where they can strategize their hunts and surround their prey to attack from multiple angles. This is usually what happens when they “hunt” sharks: one or two dolphins will grab its attention, while the others hit the shark from the sides or from behind.
While sharks are also pretty smart, they tend to do their own thing and avoid other sharks. When trouble breaks out, it’s every shark for themselves. A lone shark against a lone, unaware dolphin might win, but up against a pod, it is outnumbered.
Dolphins have very hard “beaks”
Sharks are mostly made of cartilage, which is really soft and not made to receive much direct impact, so getting hit over and over by hard dolphin snouts going full speed with the animal’s 200 lbs of strength behind it hurts a lot. The shark will most likely bleed internally and die.
Sharks have really sharp teeth, but in order to use them they have to bite the prey, and dolphins are really, really agile swimmers. The dolphins might get a few scrapes, but won’t likely die from attacking the shark. They’re also pretty relentless and will keep attacking the shark until it dies.