Green Bay Packers Pro Bowl receiver Javon Walker injured his left hamstring Sunday night and was held out the rest of the practice. "I felt something pull when I was running," Walker said, adding that he didn't consider it to be serious. Mark Roman and rookie Nick Collins, working as the starting safeties, collided hard as they defended a pass play over the middle during the 75-minute practice. Both players stayed on the ground for a few minutes before walking off under their own power. Neither player returned to field. A visibly shaken Roman wore an ice pack on the back of his neck. The extent of the injuries for either player wasn't known.