Considering there were examples of throws that he missed against the Vikings that he had just showed that he could make against the Cardinals, it makes me think it's something physical. The way he loses control and has games where he underthrows and overthrows passes we know he can make. I know Youngblood has said that he has always done this so that would mean it's mental. But if it's due to injuries he sustained as a Lion, it might be physical. We'll never know for sure, but I think it's a back or shoulder issue. To be able to make throws one week and then be debilitated the next time out, on a short week, suggests to me that he needs all 100% to make his throws consistently and when he's wore down, that little extra's not there that's the difference between laying the ball out perfectly to Jefferson and throwing it 10 yards short the very next game.
Of course, that's in addition to the terrible decision making that he also exhibits at the worst possible times.