Pleading (ask for forgiveness/apologize for what ever they think you did on the site worthy of being kicked off)with the arbitrator,webmaster,person who banned you and ask them what you need to do in order to try and get back on the site.
Try Emailing Them And Asking Why They Did It.. Did You Do.. Something Naughty.. Some Sites Are Picky.. Ask How You Can Get Back On. Fix Things Okay?
Send an e-mail to the owner of the site and ask to be re-instated.