VALDREMIA: Oh wow. It's amazing you guys are still at the game it's a very challenging game to chair actually. Ok, it'll take some explanation, so here goes.
Well, to answer your question. That rule is actually based on "context" to determine what words cannot be played out on its "own" meaning e.g. if by adding a "y" (usually) does not create another word that is out of contextual meaning then it cannot be played.
By that it would mean "trick" is about magic and say a prank, "tricky" means someone is being playful in pranks or does magical tricks on something/someone or simply sly etc. By context they are talking about the same context under tricks, playful, pranks, magic. With that in mind, that means it cannot be played.
However, the rule itself is tricky to grasps and sometimes debatable. The reason behind why it was there in the first place was because there had been lots of arguments in past games where a winning word was easily awarded to someone else simply by playing off the same word of same context over and over again: battle > battler > battles (still talking about battle/fighting)...it got to the point, too many playoffs were made and it became a lame way to win and also seen as an easy "steal" not worthy of a win by many players - it had been questioned quite a few times. Several players got really upset. Hence, a line was finally drawn to forbid such playoffs.
If you think by erasing the rule you can manage the expectations of such contentions especially where a winner is due to be made, by all means go ahead. By my experience after the numerous C1LG I've chaired, all the rules in the current version you're playing was created based on all past games' lessons and listed to protect every player's interest to as fair as possible a game, or at least try to, without shredding it naked and bare, and create unnecessary upsets.
So there it is, hope that explains.
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KARLFISCHER: Agree with my wife; if you want a smooth game you will need clear rules because you cant really depend on the English language to give clear-cut answers. There will be linguistic casualties, but the point is to have a fun game rather than plumb the intricacies of the English language.
