The federal Occupational Safety and Health Administration was investigating Sunday.
The accident happened Saturday at the "Feast of Mother Cabrini festival" in Brentwood.
Suffolk County police say the worker went under the ride - called the Scat - to fetch something for its operator around 7:30 p.m.
Police say he stood up, and the ride hit him and knocked him to the ground.
Carnival organizers identified the worker as 22-year-old Michael Austin.
Organizers say in a statement that the ride was found to be working properly. They say it will be closed for the rest of the carnival out of respect for Austin.
The Scat features riders standing in spinning baskets.
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