Trapped in my fc.

[Niwashi]

3.2 Disruption. You may not in any way disrupt or interfere with the Game experience of other players, including the disruption of Square Enix's computers and servers.
Offending player has put you at the lowest rank, which prevents you from entering the house. As you're unable to enter the house, you can't demolish your room, which means you can't leave your FC and join a new one with friends. They're harassing you AND disrupting your gaming experience.

To punish him for it as a ToS violation, they'd probably also have to know that it was done deliberately.

Removing Johnmark's access to the house (by itself, not counting all its subsequent effects) was a bit of a selfish jerk sort of thing to do, but SE is the one who put that option into the game, so using it wouldn't by itself be considered a ToS level of disruption.

If the FC leader knew that blocking house access would in turn prevent him from being able to leave the FC, and did so deliberately in order to trap him there, then I think that would qualify as disruption. But SE would need to know that the FC leader knew about that result. Unless he taunted Johnmark about it or demanded payment for being let out of the FC or something of the sort, that's probably not clear. (Given how little the FC leader apparently plays that character now, it's quite possible —even likely— he doesn't even realize Johnmark is trapped, and just thinks he hasn't decided to leave.)