Career
He played college football at Arizona. Grigsby played college football at the University of Arizona from 2007 to 2010. During his career he rushed for 2,957 yards on 572 carries with 28 touchdowns.
In 2013, he returned to college to play college baseball at Arizona Christian University.
NFL
Grigsby signed with the Miami Dolphins as an undrafted free agent on July 26, 2011. He also spent time on the Oakland Raiders and Tampa Bay Buccaneers practice squad.
Canadian Football League
Grigsby then signed with the British Columbia Lions of the Canadian Football League in May 2012. He was released by the Lions in June.
After spending a year in Arizona playing baseball, Grigsby returned to football signing with the Winnipeg Blue Bombers in 2014.
In his Canadian Football League debut he rushed for 122 yards on 21 carries. On October 15, 2014 he was released from the Winnipeg Blue Bombers, one week after he was demoted from starting running back. The starting running back duties were given to Paris Cotton.
At the time of his release, Nic Grigsby led the Canadian Football League with 9 touchdowns and was the fourth leading rusher, rushing for 744 yards.
Aside from his great opening game, Grigsby averaged only 47.9 rushing yards per game in the following 13 games with the Blue Bombers. On October 21, 2014, Grigsby signed with the Hamilton Tiger-Cats.
He played in 3 regular season games with the Ti-Cats, and both playoff games. In the regular season Grigsby totaled 146 rushing yards on 30 carries and 1 rushing touchdown.
In late February the Ti-Cats and Grigsby announced a contract extension.
On July 14, 2015, Grigsby was released by the Hamilton Tiger-Cats.