Ricky Williams picked up yardage in the AFC Championship game. (Winslow Townson / AP)

“The NFL has been an amazing page in this chapter of my life,” Williams, who has said he plans a career in holistic healing after football, said in a statement released by the Ravens. “I pray that all successive adventures offer me the same potential for growth, success and most importantly fun. I have to thank Coach Harbaugh and the Ravens organization for the opportunity they gave me this year.”

Earlier, via Twitter, he said: “Thank you all, but this ain't it, I'm gonna do something really special. ‘Be you and change the world.’ ”

Williams, 34, backed up Ray Rice with the Ravens and rushed for 444 yards and two touchdowns in 2011. In late January, Williams had said he intended to return to the Ravens in 2012, so perhaps this won’t be a lasting decision. Williams has, after all, unretired before. Facing a four-game suspension for violating the NFL’s drug-abuse policy, he retired and missed the 2004 season. He came back in 2005.

A Heisman Trophy winner at Texas, his career stats show 10,009 rushing yards and 66 touchdowns over 11 years. He also caught 342 passes for 2,606 yards and eight touchdowns. He made a huge splash with the way in which he entered the NFL in the 1999 draft. New Orleans Saints Coach Mike Ditka traded all his picks and the first- and third-round picks in 2000 to the Washington Redskins in order to take Williams with the fifth overall pick.

Williams has long planned for life after football, given the inner turmoil he was enduring. “It’s like the open-minded, spiritual person and the football player, they get into a tug of war,” he told the New York Times in 2009. “It’s not pretty. It’s ongoing. I have to find a way to reconcile both those parts of myself so that I can have some kind of peace.”