With everyone in the league knowing that AD only downfall is his inability to hang onto the ball. It is usually when AD is trying to get the extra yard or so. So many fans are enraged every time he fumbles the ball away. Peterson has many more positives than negatives. He strikes fear into every defense that he faces. The opposing teams usually stop AD in order to win the game.
There have been some great that have had issues hanging onto the ball earlier in their careers as well:
Great NFL running backs fumbles per season for his first 4 season as a pro:
After 3 season Adrian Peterson is averaging 6.67