"Not a clan server" is likely to be interpreted that the server itself is not RUN by a clan, so players would find it unlikely they'd drop in on a clan using less organized, randomly arriving public players as cannon fodder. It's obvious, using Ventrilo, or Teamspeak, the clan would have a decided advantage, and pretty much own every round. Also, there's a tendency for clans to lock squads, or boot people not in their squad.
Well, then, if that smacks of unfairness, then a squad dropping-in on a "non-squad" server to "practice" on the poor public players must be seen as having that same quality of unfairness. Should a clan drop in on a "clan" server, and squad up playing against the local clan, that would seem to even things out a bit. However, in the "pick on somebody your own size" vein, clans dropping-in on public servers to work over the unsuspecting players amounts to cowardice, doesn't it?
From what I understand about the rules for servers that keep points, it's not restricted to have a "team stacking" rule. The rules don't specifically mention it, from what I understand.
What's outrageous about this complaint is, and only a blind person couldn't see, they knew what they were doing when they came on this server, THEN, they put on an act of innocence, even admitting to giving the admin' guff when they realized their dreams of pawning the locals wouldn't be realized. That's rather disingenous, if not outright dishonest, eh?
So, yeah. Boot, and if you get guff, ban. If a clan wants to practice, they can practice on their own server, or find a server that's already "clanned-up" and "pick on somebody their own size."
Good decision. Crybabies?