Does the Grand Magic Games have referees?
It seems like the pumpkin head (the king) was the referee for the Grand Magic Games that we see, but generally, the guilds that compete aren't Dark Guilds, so they don't have a reason for sabotage.

Raven Tail was just an exception, and one of the judges (the former council member) told the guest judge (council lacky) to keep a close eye on Raven Tail.

Also, there are no rules about torturing, so Lucy vs. Minerva fight was considered a Minerva's win.