Stacy, originally a fifth-round pick out of Vanderbilt, rushed for 973 yards and seven touchdowns as a rookie with the Rams in 2013.
Stacy's playing time dropped off in 2014 and the Rams traded him to the Jets in 2015. He broke his ankle during the 2015 season and never fully recovered. The Jets waived Stacy last year after he failed a physical.
"The game of football was more than a game to me," Stacy wrote Thursday on his Instagram page. "It was a life changer. Talk about a sport that teaches you the important values of faith, dedication, commitment, perseverance, work ethic, discipline and leadership which not only shaped me into a talented football player throughout the years but into a man."
Stacy finished his NFL career with 1,355 rushing yards and nine touchdowns with 53 receptions for 358 yards and one TD
"As much as we want to as players, we can't play this game forever," Stacy wrote. "Father Time may have caught up to some. Some may have had a bad hand dealt in the business. Some had career ending injuries, like myself. Some simply felt like it was time. All different factors can play into why we leave this game but regardless of the reason, regardless of the circumstance, the game of football will always have my heart."