He played college football for the Washington State Cougars, earning recognition as a consensus All-American in 2005.
His father, Jerome Persell, was a tailback and three-time Mid-American Conference offensive player of the year (1976–1978) at Western Michigan University in Kalamazoo.
In 1978, he became the third runner in Division I-A history to reach 4,000 yards in three seasons and tied a then-NCAA record with three consecutive 200-yard performances.
After receiving a sole NFL tryout, Persell was told that he was too short and too light, a remark that Harrison would encounter as well.
On October 13, 2010, Harrison was traded to the Philadelphia Eagles in exchange for running back Mike Bell.
On October 20, Adam Schefter of ESPN reported that Harrison failed the physical because doctors discovered a brain tumor.
In it he, his wife and mother mention that he was expected to be a quadriplegic, but he had been very tenacious in his recovery and has regained many of his motor skills.