RN, with someone who's been here awhile, it's usually repeatedly attacking other members, or, occasionally, the staff (mods/admin.) Some members have been given the boot for a passive/aggressive type behaviour, for example, misinterpreting and twisting another poster's words, then getting upset when the poster flames them for doing so. When this happens once or twice or even three times, we'll let it slide. Everyone misinterprets or misreads things from time to time. But when it happens over, and over, and over, and the same poster is being reported over and over and over, it's pretty hard to ignore. After awhile, it becomes obvious that the poster doesn't have a problem with English; they're just enjoying the reaction their behaviour provokes.
As with most internet sites I'm familiar with, one offence with usually get you a warning. A second will get you a warning and a spell on moderation (your post is read by a mod before going 'live'.) A third offence may get you a longer spell on moderation, or an outright ban, depending on how serious it is. Each reported post appears in the moderator forum, where all the mods can see it, and is judged individually. If it's a straightforward, simple decision, such as solicitation, or some foul language, the first mod to see it/report it will deal with it. If it's not so simple, we usually get feedback from the other mods before taking action. No one is banned on a whim, and if a mod has been personally attacked by a poster, they will often ask another mod to deal with it, to prevent their angry/hurt feelings from affecting the decision.
First time posters who are recruiting or advertising usually get banned immediately, especially if they are spamming the boards as well. Some will come in and try to post the same message in as many forums as they can. We have 158 forums here, so you can understand what a pain it is to delete all those duplicate posts!!
A few other things may get you an immediate ban, such as posting objectionable material (e.g., links to porn sites) or really hateful flame attacks, but most often, we prefer to put posters on moderation. It's amazing how the trolls disappear when they can't get a reaction to their posts!