any serious injury from this would stand a good chance at a lawsuit

Lawyer here. I assume you mean to say there'd be a good chance at winning a lawsuit. No, there would not be. The form of release participants sign will basically be a consent to a battery. It's going to say, "We are going to hit you hard with stuff and try to maim or kill you and you consent to this."

Also, if the producers are smart, they don't say even one word about safety precautions. That will insulate them completely from claims that they somehow misrepresented things.

Finally, the release contract will recite that the participant is not relying on anything said by the producers except what is in the release document itself and that if the participant sues the producers and loses, the participant will have to pay the production company's lawyers and court costs.