Ehm...What about player that accept not to challenge themselves until they are the last men standing?
If I make a deal with some other, and we decide to try and eliminate all the other, and then see who will be the winner, is that...
...fair? I don't think so
...legal? Since rules don't ban it, so it is legal.
Sue it'll be quite difficult to control, but if you see two player involved spending the whole day in chat waiting for someone to come and not challenging togheter, what would you think?