Linebacker Reuben Foster entered his rookie season with a lot of expectations and more than a few concerns. While he has been a productive player whenever he’s been on the field, Foster missed six games due to injuries -- a high-ankle sprain and bruised ribs. But none of his time missed has been connected to right shoulder surgery he underwent before the draft. Four other times, Foster has required medical attention on the field, only to return to action without missing any significant playing time. “I mean the guy just wants to kill people,” 49ers defensive coordinator Robert Saleh said on Thursday. “So sometimes he kills himself for a play.