I guess I'll be the one to say that judge is out of line.
Was this the Head Judge that forced you to do that? Because the Head Judge is required to approve all penalties above a Warning.
Anyway, that is a
minor game play error. It does not confuse or otherwise affect the game state in any way, unless someone is just asleep at the wheel (like you trying to sneak in two Supporters in a turn). There's no way I'd give any sort of game state altering penalty for it, unless it happened
repeatedly -- that is, way more than twice.
Personally, I don't see anything wrong with putting a Trainer in the Supporter area so your opponent can clearly see what you're playing, performing the Trainer action, then moving it to the discard. I'd have a hard time finding a judge that would. Apparently you found one.
Also, there is a prescribed list of penalties -- Caution, Warning, Prize Loss, Game Loss. I don't see forcing a player to end their turn on that list. I'd love to know how he plans to report that to POP.
You can always email
[email protected] and tell them you think the judge inappropriately issued a penalty. They do track those things and take things up with the PTO if there is a pattern of poor judging.