Richardson struggled in his career following a strong rookie season after being selected by the Cleveland Browns with the third overall pick of the 2012 NFL Draft.
“Excited about this,” Richardson told AL.com about joining the AAF, which is a new, eight-team league that is scheduled to begin play in February.
“Another opportunity for my professional career. Happy to be doing something that I really love doing, especially in Alabama and in Birmingham, which is a home away from home for me.”
Richardson rushed for 950 yards with the Browns in 2012 before being traded to the Indianapolis Colts for a first-round pick, which later resulted in Cleveland selecting quarterback Johnny Manziel.
A former University of Alabama standout, Richardson averaged just 2.9 yards per attempt in 14 games for Indianapolis in 2013 and 3.3 yards per rush in 15 contests in 2014.
After being waived by the Colts following the 2014 season, Richardson participated in camps with the Oakland Raiders and Baltimore Ravens in 2015 and 2016, but he has not played in an NFL game since 2014.
Richardson ran for 2,032 yards on 614 career carries, averaging just 3.3 yards per rush while playing in 46 NFL games.
He later signed with the Saskatchewan Roughriders of the Canadian Football League before being released earlier this month to pursue the opportunity to join AAF.