I could see if someone violated some major law by doing some crazy rogue trades that blew out an account....but really, how can you sue someone for losing money in the markets, especially if you hired the to trade for you? I assume there is some degree of understanding that the prop firm was aware they were taking a risk by hiring a trader....wouldn't it be pretty hard to prove in court that they didn't understand the risks they were taking? Barring of course, the trader doing something ridiculously outside of some signed agreement of conduct. I don't know how it all works, but that's just silly to me.