Seattle Seahawks running back Chris Carson plans to retire after just five seasons in the NFL. The Seahawks released Carson with a failed physical designation but it is widely believed that the 27-year-old will ultimately decide to retire. Last month, Seattle head coach Pete Carroll speculated that Carson would have to retire due to constant setbacks due to a neck injury he sustained last season. “We visited — it was about 10 days ago now — here and had a real good chance to hang out with him and feel him,” Carroll said. “He’s concerned because he wants to play, and he loves the game, and he’s…