The cause of the malfunction is being investigated, Admiral Scorby said.

The Leap Frogs were a main attraction of a Fleet Week event billed as an educational celebration in which the public, especially families with children, could learn more about the Navy, the Coast Guard and the Marine Corps by exploring military vehicles and participating in activities.

With the Statue of Liberty and the Manhattan skyline as a backdrop, the team of parachutists descended from a helicopter around noon. Onlookers described a typical Leap Frogs demonstration, in which the parachutists join hands and twist and turn in the sky. Their yellow and blue parachutes were emblazoned with “NAVY,” and one parachutist carried a giant American flag that whipped in the wind.

But one parachutist peeled off from the others and slipped out of view.

His parachute, which never fully opened, fluttered to the ground in a nearby parking lot.

Maria Ashley, 49, a spectator, said few people around her realized anything had happened because several tall glass towers on the New Jersey side of the water blocked a view of the parachutist as he went into the river.

But Ms. Ashley said she had thought something had gone awry. “I knew it wasn’t right because the parachute should be in an arch,” she said.