Joe McKnight has shown only flashes of the speed and moves that made him one of the nation's most highly prized recruits. But after less than two weeks of practice, it is clear to USC teammates and coaches that the freshman running back from Louisiana will be an impact player this season. "We know he's a great player and what he's capable of doing," quarterback John David Booty said. "Now he's just got to go do it on Saturdays." McKnight, 6 feet, 180 pounds, has been compared to Heisman Trophy winner Reggie Bush, especially as a receiver and multipurpose threat.