Clinton Portis has a ton of heart. He will do anything you ask him whether it be running, blocking or catching (or at least attempting to) the football. However, Portis just isn't the same back as he used to be when it comes to finishing off runs and getting through the secondary.
Now, Portis seems to have a new problem: he's afraid of contact.
Today against the Rams, Portis seemingly tackled himself while breaking a run into the St. Louis secondary. It was a nice, long run, but Portis fell down instead of slamming into the defender for extra yards. Portis has been shying away from contact all season, and this 27-yard run during the first quarter was a prime example of Portis simply not finishing runs for whatever reason.
Maybe it's the fear of sustaining another concussion after he suffered one last season against Atlanta. Maybe it's just an aging back who has lost his edge. Whatever the reason, Portis can't rip off big runs anymore, and he looks uncertain as to what to do when he does get more than 10 yards downfield.