Stacy earned Vanderbilt’s MVOP award (Most Valuable Offensive Player) and set the single-season record for rushing with 1,193 yards, breaking a mark set by Corey Harris in 1991. He also broke the record for rushing TDs with 14. Stacy ended the year as the 3rd-leading rusher in the SEC, earning 2nd team All-SEC honors. In 2011, he was the 4th person all-time for a Vanderbilt player to rush for over 1,000 yards (1072), and first since 1995 (Jermaine Johnson). Stacy had the most rushing attempts (201) since 1995 (Jermaine Johnson) (267) moved up to 8th on all-time Vanderbilt rushing yards in a career (2,002), and averaged 91.8 rushing yards per-game (YPG) and 117 YPG at home. He tied with Allama Matthews TE, 1982 with most TDs totals by a single player with 14. He ranked 2nd all time with 84 points, tied with Matthews behind Jack Jenkins (90) points in 1941, and rushed for 3 TDs 3 times vs. Army, Kentucky and at Wake Forest Had his second 100-yard game against Ole Miss. He completed first pass of his career, passing to Jordan Matthews for a 43-yard TD pass, and had 198 rushing yards against Army, 128 yards against Arkansas Season-high 28 carries against Kentucky and again at Wake Forest. Stacy was named the SEC Offensive Player of the Week for 135-yard, three-score performance against the Wildcats on Senior Day. He ran for 184 yards at Wake Forest to break team single-season record, and scored in seven of team’s final eight games.

At Vanderbilt, Stacy made his first career start as a true freshman against Western Carolina due to an injury to starting tailback Jared Hawkins, who was sidelined with a bad foot. Stacy teamed with Warren Norman, with the pair combining for 240 yards on the ground. It was the first time in school history that two freshmen had rushed for over 100 yards in the same game. Stacy’s total of 135 yards was a school record for a freshman. Norman, alternating series with Stacy, also went over the century mark with 105. Stacy played in 10 of the 12 games in 2009, starting 4 games. He missed the games against Ole Miss and South Carolina with a lingering ankle injury that also limited his production against Mississippi State and Rice. He finished the season as the team’s second-leading rusher behind Norman with 478 yards and three touchdowns on 107 carries.

Stacy was drafted in the fifth round with the 160th overall pick in the 2013 NFL Draft. In his first NFL game, Stacy had one run for 4 yards and no receiving yards against the Arizona Cardinals. He got his first start on October 6, 2013, against the Jacksonville Jaguars but was forced out of the game in the fourth quarter due to a rib injury. He was the leading running back in the game with 14 carries for 78 yards. In Week 6 against the Houston Texans, Stacy gained 79 rushing yards on 18 carries.

On October 28, 2013 on Monday Night Football, Stacy had arguably the best game of his rookie season against the Seattle Seahawks, getting a season high 134 rushing yards on 26 carries. The following week, Stacy turned in a second 100+ rushing yard game in a 28–21 loss to the Tennessee Titans, with 127 yards on 27 carries and two touchdowns. The two touchdowns were his first career rushing touchdowns and the first rushing touchdowns for the Rams during the season. He also had six catches for a career-high 51 yards.

Shortly after the Rams selected running back Todd Gurley in the 2015 NFL Draft, Stacy requested to be traded. The Rams traded Stacy to the New York Jets in exchange for New York’s 2015 seventh round (224th overall) pick on May 2, 2015. On November 12, 2015, Stacy broke his ankle against the Buffalo Bills and was placed on injured reserve the following day.

Stacy was waived by the Jets on July 27, 2016 after failing his physical.

On February 16, 2017, Stacy announced his retirement from the NFL. The early retirement was due to injuries and also to take care of his brother, who has Down Syndrome.

On May 20, 2018, Stacy officially came out of retirement and signed with the Saskatchewan Roughriders of the Canadian Football League. Stacy played in, and was his team’s leading rusher in both preseason games; he accumulated 51 yards on 11 carries, in addition to catching 3 passes for 39 yards. Despite this, Stacy lost out to recently signed former teammate Tre Mason, who had only one carry in the only preseason game he appeared in.

January 2019, Stacy signed with the Memphis Express of the newly-founded Alliance of American Football for the 2019 season. CBS Sports reported in February 2019, shortly before the 2019 AAF season was set to commence, that Stacy was expected to be among the “names to watch” for the Express in the upcoming season. In the Express’ week one 26-0 loss to the Birmingham Iron, Stacy rushed 12 times for 58 yards.

On February 16, 2019 against the Arizona Hotshots, Stacy rushed for 101 yards before he was pulled out of the game, becoming the league’s first running back to eclipse the century mark. Stacy was placed on injured reserve on April 1, 2019; the AAF announced shortly thereafter that it was suspending all football operations. In 8 games played, Stacy rushed for 317 yards and 3 touchdowns on 100 carries, and caught 18 passes for 138 yards and another touchdown.