Former defensive tackle Christian Ballard says there is no deep, dark secret about why he abruptly left the Minnesota Vikings during training camp. He's not mentally or physically ill.

Christian Ballard walked away from the Minnesota Vikings and the NFL. (Charlie Neibergall / Associated Press) By Houston Mitchell . Sept. 18, 2013 8:04 AM PT . Share via Close extra sharing options.

Minnesota Vikings defensive tackle Christian Ballard makes his way to the field during NFL football training camp, Monday, July 29, 2013, in Mankato, Minn. (AP Photo/Charlie Neibergall) AP The ...