Grimes played running back at the College of William & Mary from 2008 to 2011. He started all four years and became the school's leader in rushing attempts, rushing yards, kickoff returns and all purpose yards. Those totals were good enough to rank him third all time in the Colonial Athletic Association for all purpose yards and sixth all time in rushing yards. During his senior season Grimes led the nation in all-purpose yards per game. He won a number of awards that year including Associated Press All-American, College Sporting News All-American, Sports Network All-American and finished fourth in the final voting for the Walter Payton Award.
Professional career
Pre-draft
At his 2012 Pro Day, Grimes ran a 4.53-second 40-yard dash which would have put him in the top ten among running backs at the NFL Combine that year. He also had a 10-foot 5-inch broad jump and a 38-inch vertical jump, both of which would have been good enough for second place at the combine for his position.
Houston Texans
Grimes was not selected in the 2012 NFL draft. However, he was considered a high-priority free agent and 10 NFL teams offered him a contract right after the draft. Grimes signed with the Houston Texans on April 29, 2012, as an undrafted free agent. In his preseason debut against the Carolina Panthers, Grimes scored a 3-yard touchdown, Houston's lone touchdown of the game, and finished with 37 yards on nine carries. Grimes was limited in Houston's second game against the San Francisco 49ers, carrying the ball twice for 22 yards. Grimes again saw limited action the following week against the New Orleans Saints. He carried the ball 4 times for 22 yards with the starters playing most of the game. In the Texans' last preseason game versus the Minnesota Vikings, Grimes carried the ball 13 times for 49 yards. Grimes was waived on August 31 and signed to the practice squad the following day.
Grimes was signed by the New York Jets from the Texans' practice squad on September 25, 2012. Grimes was activated for his professional debut against the Houston Texans on October 8, 2012. However, he saw no playing time. Grimes was waived on October 30, 2012. He had two carries for six yards over three games.
Houston Texans (second stint)
Grimes was re-signed to the Texans' active roster on November 1, 2012 after Ben Tate suffered a hamstring injury. Grimes was waived on December 20, 2012 after primarily playing on special teams.
Grimes was signed by the Jacksonville Jaguars on December 21, 2012. He was released by the team on August 30, 2013.
Houston Texans (third stint)
Grimes was re-signed to the Texans' active roster on December 18, 2013, after Ben Tate was placed on injury reserve. In Week 17 of the 2013 NFL season against the Tennessee Titans, Grimes started his first game, rushed 16 times for 50 yards, and had 6 receptions for 76 yards as the Texans lost by a score of 16-10. In 2014, Grimes rushed for 153 yards and caught 6 passes for 86 yards. In 2015, Grimes rushed for a career-high 282 yards and had a career-high 173 yards on 26 receptions. On January 3, 2016, against the Jacksonville Jaguars, Grimes became the third player in Texans history to score a rushing and receiving touchdown in the same game. In the postseason, Grimes played and started his first playoff game, rushing 4 times for 15 yards and catching 2 passes for 12 yards. On March 18, 2016, Grimes signed a one-year contract worth $900,000 to remain with the Texans. Grimes rushed for 105 yards and caught 13 passes for 94 yards. In the postseason, Grimes played in both playoff games, rushing 10 times for 56 yards and catching 4 passes for 43 yards.
Jacksonville Jaguars (second stint)
On August 11, 2017, Grimes was signed by the Jacksonville Jaguars. He was released on September 1, 2017.
Personal life
Grimes is an avid singer and piano player. He started playing piano at age 7 at his father's insistence. He has two older siblings, a sister and a brother. He composed the opening theme and co-hosts Arian Foster's "Now What?" podcast.
