Ok… everyone saying Meads or Rebecca, but noone talking about Cavendish (yeah some of you mentioned him, but look at the poll, he got only 7%). I know that nothing indicates he did anything, buuuuut, he was portrayed to be somewhere about level of Don (maybe higher we don't know), and Rebecca was pictured as pretty weak, owned easily by Luffy who didn't even try (ok she didn't try too much either, but still), bullyed by other contestants, and taking her time with fodders, panting etc. So it really is hard for me to believe that she suddenly awakend such power when she could own everyone and pass out. Ok i can take it that she got some skills and could own tons of fodder, fine. But own fodders + some mentioned gladiators who werent push overs and freaking cavendish who was shown to be quite strong? I can't believe it, and for now it seems really weird/bad that he's out.... unless we get really good explanation next chapter..
But I also doubt he has attack like that (destroy everyone and pass out for a moment). So the only thing that makes sense to me is that they got haxed somehow, just like sleeping gas etc. Or they are owned by someone incdredible strong. But even then, for someone to destroy Don level of fighter and others so effortlesly in an instant would take what... Admiral or Younkou? That seems unlikely too..
So all in all I don't know what happened, but im hoping that Cavendish is standing up in the end, because after all the hype he got it would really be anti-climatic for him to lose so easily...