^This is extremely unfair on West Ham. They registered a player, his documents weren't in order. The FA's procedures did not discover that until later and they then fined West Ham a significant amount of money.
The FA chose to fine West Ham, not to dock them points. That is their decision. No court of law can decide that Carlos Tevez's presence caused West Ham to win or lose football matches. Tevez and Mascherano were extremely disruptive early on and quite possibly caused West Ham to be in a relegation battle to begin with.
My understanding is that Tevez is on a two-year long loan deal with Manchester United. His registration is still owned by Media Sports Investments. Either the FA and FIFA allow third parties to hold player registrations or they do not.