With over half the NFL regular season in the books, the wheat is being separated from the chaff. While some teams have surprised us, others are where we expected them to be all along. It has left us with eight teams with six wins or more, and all eight will be thinking what could be come Feb. 2, 2014, when New York/New Jersey hosts the Super Bowl.

But that's not all they will be thinking about. Because the journey to get there is still a long one and each team will have identified some key weaknesses that they'll need to improve on during the stretch run. So this week we're going to help them out and break down the weakest link in the starting lineup and explain why they're a problem for the weeks ahead. And as Kansas City shows us, even perfection has a potential big flaw.

Kansas City Chiefs: Alex Smith, QB (2013 PFF Grade: -6.6)

The Chiefs may be 9-0, but the arm of Smith has hardly been tested this season. Smith is a player who has just enough talent that he can get by with a special defense (and the Chiefs D is special, as they comfortably are our highest-ranked defense). As the poor results under Matt Cassel showed us, Smith's achievements are still notable, but it means when the schedule toughens up (as it will over the next month), Smith's flaws are likely to be exposed. Smith is our fifth lowest-ranked pure passer and it's easy to see why, with a style that is more reliant on dumping the ball off than making plays downfield. It's telling that his yards-in-the-air percentage of 44.9 is the lowest in the league, meaning the Chiefs have the highest percentage of yards after the catch of any team in the league. Eventually Smith will need to beat teams down the field if the Chiefs are trailing -- and that's not his game. He's throwing just 5.7 percent of his attempts further than 20 yards, the lowest rate in the league and an indication of how limited the passing attack is.

Seattle Seahawks: Paul McQuistan, LT/LG (-19.9)