It really depends. If the random player who gets in is trying to do the fight, not intentionally griefing or causing a problem, I think they'd be 100% in the right to report someone who, for example, deliberately killed them with a tankbuster and then refused to raise. On the other hand, if the sniper is the one causing problems, I don't think it will end well for them. But this all seems difficult to prove either way unless there's video or something is said in the in-game chat.