Reporting a cheating commissioner
This article explains that in Private leagues, Yahoo! does not get involved in disputes, and commissioners have complete control in those leagues.
All custom league matters must be addressed to the commissioner. We recommend that you attempt to contact your commissioner via email or your league's message board to resolve any disputes. Yahoo! Sports will not act as a go-between with commissioners and managers in any way.
We also will neither remove nor restore teams from private leagues. You are not obligated to visit the team or league pages if you no longer wish to participate in your private league.
We will not interfere with private leagues. We invite you to join one of our public leagues. In a public league, you will be matched against other players from across the globe that will be randomly assigned to your league. There are no commissioners in public leagues.
You may also take advantage of Yahoo! Fantasy Sports Manager Rating System. The Manager Rating System will enable you to rate other managers (including your commissioner) in your league (Positive, Neutral, or Negative) and provide a short comment about your experience playing with them.