Bills Star Leaves Field After Injuring Hamstring Buffalo receiver Stevie Johnson left practice after injuring his left hamstring Friday morning. Johnson, Buffalo's top receiver, pulled up on a route during a red-zone drill two hours into practice. He was evaluated by Buffalo's training staff, and he was assisted by two people as he walked slowly to the locker room. Bills Coach Doug Marrone said after practice that he did not know the severity of the injury. Johnson has had issues with injuries in recent years. He missed several practices in the spring because of a back injury and had groin surgery last off-season. Any prolonged absence would be a concern because Buffalo is trying to establish a fast-paced, up-tempo system under its new offensive coordinator, Nathaniel Hackett. Johnson, coming off three consecutive 1,000-yard seasons, is the team's only established receiver. GIANTS ROOKIE HAS CONCUSSION Justin Pugh, the Giants" first-round draft pick this year, sat out practice with a concussion sustained Thursday. "He had a headache this morning," Coach Tom Coughlin said, adding that Pugh, a backup tackle, was going through the standard concussion protocol of testing and examination. He'll be out until he passes all of that. Earlier, Giants wide receiver Hakeem Nicks, who has been limited in practice this week with what the team has described as tightness in a groin muscle, said his injury was not serious. "Coming off last season," Nicks said, referring to the knee and foot injuries that inhibited his play in 2012, "I'm playing it safe and cautious. I've got to protect myself from myself. I want to take it slow and not have any serious setbacks. My knee and foot feel great. I just want to be careful in training camp so I can perform when it counts. RAVENS" JACKSON SUSPENDED Baltimore cornerback Asa Jackson has been suspended without pay for the first eight games of the regular season for violating the N.F.L."s policy on performance-enhancing substances. "My reaction to that is that you've got to follow the rules," Ravens Coach John Harbaugh said after practice, adding, "That's a fair rule, there's no place for that, and he's getting what he deserves." Jackson received a four-game suspension as a rookie last season for the same reason. 49ERS" CULLIVER TEARS A.C.L. San Francisco 49ers cornerback Chris Culliver will miss the season with a torn anterior cruciate ligament in his left knee. Culliver, who was San Francisco's third cornerback the past two seasons, was injured Thursday during a noncontact drill. RICE BACK IN SEATTLE Seahawks receiver Sidney Rice, who flew to Switzerland to receive a plasma injection in his knee to help with patella tendinitis, has returned to Seattle. Rice was mostly a spectator Friday as the Seahawks held a scrimmage. Coach Pete Carroll said Rice was expected to return to practice Sunday. JAGUAR MAY HAVE CONCUSSION Defensive end Jeremy Mincey, who has started the last 40 games for Jacksonville, has been sidelined with a possible concussion. Coach Gus Bradley said Mincey had a "head contusion," adding that Mincey was seeing a neurologist for more testing. STEELER HAS MINOR SURGERY Pittsburgh Steelers cornerback Cortez Allen had minor surgery on his right knee. Coach Mike Tomlin said the procedure would have no long-term effects and estimated that Allen would be out for a couple of weeks. The Steelers are expecting Allen to take over a starting spot. CARDINAL WON'T BE OUT LONG A sprained knee ligament that forced Dan Williams, Arizona's starting nose tackle, off the practice field was deemed not serious, and he said he expected to be sidelined for only a few days. Williams also sprained his right ankle on the play in Thursday's practice, an injury that Coach Bruce Arians said would probably wind up being worse than the knee injury. BIRK TO BE APPEALS OFFICER Matt Birk, a center with Baltimore last season who recently retired, will replace Art Shell as one of two appeals officers approved by the N.F.L. and the players union. AROUND THE LEAGUE San Francisco signed receivers Austin Collie and Lavelle Hawkins to one-year deals after they worked out for the team. ... Oakland signed kicker Sebastian Janikowski to a four-year extension. ... Cleveland running back Trent Richardson missed practice because of a bruised right shin, but Coach Rob Chudzinski said it was strictly a precautionary move.