NFL running backs running into shorter careers

When the Broncos rattled the NFL’s sensibilities with a rare blockbuster, star-for-star trade in March 2004, Clinton Portis was a 22-year-old franchise-back-in-waiting, a player with nothing but sunshine over the horizon and two 1,500-yard rushing seasons already on his resume.
Six seasons later, the Broncos will play Portis’ team today, and Portis will not be in uniform. He has played much of this season on sore ankles and is recovering from a concussion.