While totally terrifying -- the video shows someone from the boat crew opening the cage door, so the trapped diver can escape the perilous situation -- the video’s caption depicts a slightly calmer scene.
“What might appear to be an aggressive great white shark trying to attack the cage, this is not the case,” the description explains. “These awesome sharks are biting at large chunks of tuna tied to a rope. When a great white shark lunges and bites something, it is temporarily blinded. They also cannot swim backwards. So this shark lunged at the bait, accidentally hit the side of the cage, was most likely confused and not able to swim backwards, it thrust forward and broke the metal rail of the cage.”
Although rattled, the “very experienced diving instructor” was totally fine after contending with the panic-inducing event.