ALLEN PARK -- Detroit Lions running back Sione Vaki’s season debut lasted only seven snaps on special teams in Baltimore. The second-year pro exited late in the first half and did not return due to a groin injury. But the special teams standout has been unable to stay on the field to open his sophomore campaign. “I don’t know,” Lions head coach Dan Campbell said of Vaki’s status. But it’s Vaki’s absence on special teams that leaves a vital role to fill.