FrancescoLR: Sorry I never got a chance to answer before... but will try to jump in here and help a little if I can.

The best thing might be to be around when the tournament is ready to start, and before it starts - kick out any players that are not suppose to be there - since as Vikings said, once it starts, there is really no way to remove anyone. (weather Fencer will not give out a prize to someone would be something you would need to talk to him about.)

One thing you could do is a few hours before a tournament is set to start, look at the list - remove the players, and even change the "start time" to a time that has already past - which would mean that when the tournament start-up script runs within the next hour, the tournament will start... hopefully without anyone who is not suppose to be in there signs in.

Other idea - make it an invite only tournament - and if someone wants to play, have them send you a message where you can invite them