Posted by ESPN.com's James Walker
The wear and tear of playing in the trenches simply took its toll on Anderson, who gutted out a solid 2008 season in which he played some of his best football in recent memory. He's been dealing with knee and leg issues since his time with the Cincinnati Bengals, and at age 33, Anderson could no longer grind out another season.
An educated guess is the Ravens saw this coming. Last month they traded up in the first round to get Oher, which is a sign the team sensed a big question mark at the position. It is unknown if the team expected Anderson to retire, but the Ravens definitely wanted competition and insurance at the position.
Now that insurance policy in Oher is being cashed in right away.