Former South Carolina running back Marcus Lattimore signed a four-year contract with the San Francisco 49ers on Friday. Terms of the deal weren’t disclosed.The second of the 49ers’ two fourth-round draft picks, Lattimore is feeling stronger each day as he recovers from a serious knee injury.Lattimore told The Associated Press about his rehab and said the most difficult part has been doctors and trainers slowing him down from overdoing things. Lattimore still believes he can be ready to play this fall, but is content to follow doctors’ orders.“I just want to train as hard as I can,” Lattimore said. “But I understand why they want me to slow down.”Lattimore overcame a torn ACL as a sophomore to return to the field last season. His college career, though, ended for good against Tennessee last October when Lattimore dislocated his right knee and tore three ligaments. He had surgery a month later and declared for the NFL Draft in December.Lattimore finished his college career as South Carolina’s career leader with 38 rushing touchdowns.Lattimore’s focus these days is getting back to the football field at a pace that works for his new team. San Francisco coach Jim Harbaugh has said he wants Lattimore to take a slower approach. Briefly • Chiefs: Running back Jamaal Charles suffered a toe injury on his right foot and left Friday’s practice early, according to the Kansas City Star. X-rays came back negative and Charles could return when a three-day mini-camp begins on Tuesday. • 49ers: Quarterback Colin Kaepernick made a surprise appearance at his alma mater, Pitman High School in Turlock, Calif., during commencement ceremonies Thursday. Kaepernick was there to bid farewell to football coach Brandon Harris and teacher David Jack. “I had to come back to say goodbye to two of my favorite teachers and also congratulate the graduates,” Kaepernick said. • Rams: Running back Isaiah Pead will serve a one-game suspension at the start of the season for violating the league’s substance-abuse policy, according to NFL Network. A second-round pick in 2012, Pead is a contender for the starting job left vacant by Steven Jackson’s departure. • Media: Former Buccaneers defensive back Ronde Barber will join Fox Sports in what Barber’s agent called a “hybrid role” that could include game analysis and studio analysis on its new Fox Sports 1 channel.