I like the way they do it in cricket. If the official isn't 100% certain a mistake has been made he leaves the call with the onfield official. IMO it would eliminate 90% of the wrong decisions. For example the Ashley Young sending off would have stood because it's not 100% clear, however Fulham would have got a penalty because it WAS 100% clear that Murphy was fouled. 1 challenge a half, if challenge is overruled it is gone, if you win you keep the challenge. Good point, so it is a clear cut one after all