Spearfishing is a tricky sport. Those sharks can smell the scent of blood from an injured fish that is caught from miles away, but their seeing isn't so great so sometimes they go after the wrong target, like the fisherman instead of the fish.
This guy was spearfishing in Key West when an 8 foot reef shark attacked him and it was all caught on a GoPro that he was wearing.
The fisherman is OK, but also lost more than two pints of blood from the bite.