Marshall intended to spend his college playing career with the University of Miami, but was not accepted due to academic reasons.
In 1999, he began attending the University of Oklahoma as a criminal justice major, and was co-captain of his football team for two consecutive seasons.
He was named MVP of the 2001 Orange Bowl, in which the Sooners defeated the Florida State Seminoles to win the national championship for the 2000 season.
During the 2002 season, he began seeing action at fullback as well as linebacker when starter William Henderson was battling injuries.
After taking the 2005 season off, Marshall joined the Austin Wranglers of the Arena Football League as a fullback/linebacker.