Coney Island Beach in Brooklyn GIGANTIC Jellyfish. Do you know which Jellyfish this is?

I was walking on the Coney Island Beach in Brooklyn on an early Sunday morning on July 19th and I thought I was looking at a plastic bag inflated with air and water, but I was wrong. I was looking at a GIGANTIC jellyfish at the water's edge, tumbled by waves and flipped upside down and all around. I wasn't sure if it was dead or not so kept a safe distance. I saw another one further down the beach and a woman picked it up with both hands and threw it back in the ocean but it looked dead. I have no idea if it is poisonous or not and I didn't want to put my health at risk by doing the same. Does anyone know anything about these jellyfish? What kind is it? It was GIGANTIC!!!