From this story on capecodonline.com:
State marine biologists believe a great white shark was the likely predator that bit a man Monday as he swam in deep water at Ballston Beach. The man, identified as Christopher Myers, had severe cuts to his lower legs. He was being treated Tuesday at Massachusetts General Hospital in Boston, a hospital spokesman said. The last confirmed injury in Massachusetts by a great white shark occurred in 1936, state officials said.