Although he and his family moved to Tustin, California when he was one year old, Foster continued to visit relatives in Charlotte regularly as a child.

As a senior in 1997, he was named the USA Today California Player of the Year and finished the year rushing for 3,998 rushing yards and a state single-season record 59 touchdowns on a Tustin football team that finished runners-up in the state championship against a Santa Margarita Catholic High School team with quarterback Carson Palmer.

[2] Foster played football at University of California, Los Angeles (UCLA), where he set a team rushing record for true freshmen with 673 yards and 10 touchdowns on 126 carries in 11 games.

The next year, he spent mostly on the bench with an ankle sprain, but still managed to record 375 yards and 6 scores on 111 carries.

However, he returned the following season as a complement to Stephen Davis; whose bruising style matched well with Foster's speed.

The following season looked promising for the Panthers, but many of the starters suffered season-ending injuries, and Foster was no exception.

He led the team in rushing attempts and yards the next two seasons, increasingly splitting time with DeAngelo Williams.

[7] On February 29, 2008, the San Francisco 49ers signed Foster to a one-year contract worth around $1.8 million, to be a back-up behind starter Frank Gore.

On February 12, 2024, Foster was hired as UCLA's head coach,[10] signing a five-year contract for $3 million in the first year with annual increases of $100,000.