Fetishdj, I'm not sure about not legally consenting to harm. I mean, people get pierced and tattooed and have elective cosmetic surgery. I think that, in general, although it differs in some states, battery is an unconsensual touching of a certain kind; you can generally consent to physical contact, even violent contact, again with some exceptions.

What you can't do anywhere is contract away your ability to withdraw consent in the future. You can't actually play without a safeword, legally, because the ordinary words, stop, no, I don't consent will be construed as a withdrawal of the earlier consent NO MATTER WHAT was previously agreed about the meaning of those words. The perpetrator might argue that he misunderstood and therefore did not intend to transgress the withdrawal of consent, but he will be on very shaky ground.

This is not given as competent legal advice; please don't structure your life around this, but I don't want people to think that you can't give consent to rough stuff, ever.