The Green Bay Packers have a new defensive coaching staff that is charged with implementing a new defense. But while their role is perhaps the most prominent key to the success of the team in 2009, it comes down to the players on the field.To that end, there are five positions that come in as potential weaknesses for the Packers. In each case, there are players on the roster the team realistically hopes can step up to keep them from being areas opponents can exploit.The Packers have the poten...