1. As someone who didn't follow the entire ladle, my thoughts on counter-measurements aren't really systematic because I'm not sure what exactly happened and who is involved (Flex summed most of this up, but his questions aren't fully answered yet). That would be the first step to help greatly before we get this sorted out: just making a list of the events that happened and the resulting issues we need to address here. I'd find it short-sighted to approach these problems case-by-case, then we'd only leave these decisions until another ladle gets screwed up.
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2. I still think we shouldn't fundamentally change the ladle rules or punish someone based on the (from what I got...) limited knowledge we now have (although they would actually deserve that). We shoot ourselves in the foot if we make the access to the tournament too complicated or forbid aliases. Our nicknames are already aliases themselves.
(For what it's worth, I used an alias this ladle and to my knowledge didn't cause trouble...sinewav pretty much said everything about the necessity and feasibility of excluding aliases in his last post)
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3. As I said earlier, the fort clans' size/success etc depends a lot on the Ladle, and they simply have to realize that harming its reputation
in any way will also affect their own. If I'm correct the players in question currently aren't part of any clan and hence don't have to care about that, but the team captains have. They simply have to refuse to let such players play when they know they played already, even if that lowers their
individual chances to win (just) one ladle - it also assures them that there will be many more ladles with the other participants and organizers enjoying their role.
In any case, I think the ones to be held responsible here should be the team leaders, not the players.
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4. Assuming that my 3. is correct, I'd say what we need are team leaders (ideally the ones who have just lost) checking whether other team leaders don't let their/other team's players play another time. I don't know if there's a simple way to check that but doing it will be in their own interest since they wanted to beat those teams when it was still possible, so ideally there already is some kind of competition/willingness to control/"positive kind of mutual distrust". If they don't, they don't - but they harm themselves in the long run.
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5. Now the question is, what does a team leader have to do when he finds out that another team leader either a) ignores this or b) simply doesn't know someone has already played? On one side, nobody likes to restart/delay the entire tournament because of one or two twerps, on the other you can't continue as if nothing has happened.
In accordance with this, I'd suggest the following actions:
a) If it's absolutely clear that the player already played for another team (because he's using the same name), the captain
and the teamhopper are kicked during the match. The match is restarted if their team is winning.
They have to play with 4 players for the rest of the ladle. Even the best teams will have a significant disadvantage thanks to that and it doesn't matter how many players they have signed up and who uses aliases.
b) The teamhopper is kicked during the match and the match will be restarted if the team which let him play is ahead (if the other team is significantly ahead, it doesn't really matter that much, does it?). The other team has to play with 5 players for the rest of the ladle.
This wouldn't be as bad as a disqualification but it still discourages team captains from using a player signed up for someone else, since their whole team would have to deal with the consequences - it is relatively fair.
In theory, a team that violates this rule repeatedly during a single ladle just has to give up one more player every time the violation is proven.
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6. But what if all this cheating is becoming known shortly after the ladle is over?
Proposal: let the teams in question play with 5/4 players (see 5.) in the
next ladle, reschedule the finals if necessary, and give the team's seed to the next best team that didn't cheat and had the biggest disadvantage from this behaviour.
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7. Also, I'm not sure whether a ladle authority wouldn't become obsolete as soon as two people share their password (so someone can always play under a different name using that name's GID)? You would again have to compare the IPs to be sure. This applies for all GIDs, not just the ones that are specifically created for the ladle (e.g. "I have about 12 different ones but only 3 are used frequently - so it wouldn't matter to me if someone else has access to the other 7 if my team benefits from him playing under my name while I watch it, not logged in but using a random alias" - sorry in case that was a confusing example.).
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8. Another proposal that probably requires coding:
Find an easy (and preferably anonymous) way to automatically compare IP addresses of the players. The wiki IPs won't matter because people know how to use proxies, but it's clear that nobody is really able to play like that. Then perhaps you could automatically prevent people with the same IP bound to a certain alias to play for another team. But hey, I have no clue what it takes to program this.

The biggest advantage of this would be that you don't have to think of new rules or punishments since it's impossible to violate (unless you're a hacker, perhaps). The disadvantage is, well, someone would have to program it. And this will again require you to pay attention to a few exceptions, i.e. two players using the same connection (Hamar/Six; rugkei/safariskater etc.) but I think most "tron-siblings" know what integrity is and wouldn't abuse that.
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9. Out of my experience I believe subs are essential to keep the number of actually participating teams as it is. We heavily relied on our subs in practically every second ladle we played and rarely had the line-up we thought we would have, even if I met the "core players" on that ladle day some didn't show. I'd leave those rules untouched.
In one of the ladles where PRU lost the first round I was later notified that one of our subs had played for a different team after we had lost (not actual clan members) but at the time I got that notification I couldn't do anything about it anymore. And bringing it up here wouldn't have helped anyone either (by that time they also lost as a part of that other team). This is still an exception though. My only consequence then was not to talk about it and not ask that player for help again. That other teamleader knew exactly that he had someone from us on his team (and I'd bet most spectators knew it too).
This should be considered as well: I think something like my proposal in 8. could avoid this dilemma and save us a lot of nerves.
So here's my attempt to rationalize this, I'm really burned out now.