Some players come into this league with the starting job in their back pocket. That wasn't the case for Darren Sproles. He fought through injuries and criticism to make it on an NFL team. With this most likely being L.T.'s last year as a starter, the Chargers need a solid, game-changing back. When given the chance, Darren has made the most of it and is deserving of a starting role.
As for the criticism about his size, many other "undersized players" like Darren have made it in the NFL. Wes Welker, Steve Smith, and Bob Sanders are perfect examples. Even the very best of running backs don't have the ball EVERY run. So there is absolutely no reason for saying that he's not an every down back. If he gets tired, give him a break.
As a hardcore Chargers fan, I'm sick and tired of AJ Smith letting some of our best talent go in free agency. They need to tighten their belt and sign Sproles to a large contract. This kid has the talent to hang with the best of them.