More details on the incident...apears it was the hook:

"Wild was on the recreational boat with Wenner the day of the accident, 1.5 miles off Waikiki Beach. The high-performance skiff, which capsizes easily if not moving forward, had already capsized five times that day. On the recreational boat were teammates, instructors — all experienced sailors.
Wenner, wearing a harness, was standing off the edge of the boat. When the boat started to tip, he knelt down, and the harness hook got caught in the weblike netting that stretches between the hull and the outriggers of the boat, Wild said.
"Almost immediately someone from the chase boat jumped off and tried to save him," Wild said. Everybody already in the water dived down and "tried as hard as they could to free P.J."
It took a while before they figured out where the problem was.
"It was twisted so tight, we couldn't free that," he said. "We were all diving underneath," Wild said, but without goggles "we couldn't see how to free him."