This video shows sharks, probably blacktip reef or spinner sharks, attacking a school of menhaden en masse. These species don't eat people, but this is the sort of situation that occasionally gets a person hurt. In water churned by the struggles of predator and prey, visibility is bad. When that happens near the shore, people who are swimming or wading can get bitten. That's what happened to Debbie Salamone, whose story I told in Shark Attacks.
Thanks to Croconut for the tip.