If you are still in the league, click on the managers tab and click on rate manager and call him out for cheating there. e-mail the others in your league and have them do the same. Eventually Yahoo will finish compiling these rankings and list them on that persons fantasy profile (comments and all). It's not much, but at least it's a warning to anyone who plays with this guy in the future. You can contact Yahoo, but they don't usually do anything if it's a private league.