Bush received an athletic scholarship to attend the University of Southern California, where he played for the Trojans from 2003 to 2005 under head coach Pete Carroll. When Carroll recruited Bush he envisioned using him as a five-way threat. The freshman quickly proved effective in carrying, catching, throwing, and returning the ball. Bush was a consensus first-team Freshman All-American selection in 2003, and became the first Trojan since Anthony Davis in 1974 to lead the Pacific-10 Conference in kickoff returns. His 1,331 all-purpose yards set a USC freshman record. The ESPN Pac-10 Newcomer of the Year also amassed 521 yards rushing that year, with three touchdowns on 91 carries.