Following six seasons with the Houston Texans, defensive end Mario Williams entered the 2012 offseason as the prize of the free-agency class. He was an elite player at a position that -- on the whole -- is among the most coveted and well-compensated on the open market. Four years later, Williams is again a free agent. The circumstances are different, as he is now 31 years old and coming off of a disappointing 2015 season. But in a league always on the hunt for pass-rushers, veterans can revive their careers in new surroundings. Among the recent examples: Dwight Freeney (8.0 sacks last season in Arizona after two seasons in San Diego following his brilliant Colts tenure) and Julius Peppers (10.5 sacks at 35 years old in Green Bay).