Matt Cassel’s starting, but Vikings aren’t sure about their running backs

Christian Ponder has recovered from his concussion, but Matt Cassel’s still going to start at quarterback for the Vikings this weekend. That was the word from coach Leslie Frazier when he addressed the media on Wednesday. Cassel has completed 37-of-71 passes for 508 yards, three touchdowns and an interception since taking over for Ponder during…