The 49ers placed Ian Williams, who began last season as their starter at nose tackle, on the physically-unable-to-perform list today. Williams was injured early in the second game of the season when he was cut block by Seahawks guard J.R. Sweezy. The hit did not result in a penalty at the time, but it would this year after a rule was passed this offseason that penalizes blockers from rolling up on the back or side of the legs of a defender.