As far as I know there's no base feature that allows anyone to ban a user. There are some mods available that enable banning in some form ; the IP ban mod, and the user 'probation' mod. I haven't seen the IP ban mod yet, but I guess that if it currently only allows admins (mlev=4) to ban users, it would be rather easy to change to allow moderators (mlev=3) to do the same.<