A federal judge has cleared the way for Minnesota Vikings running back Adrian Peterson to be reinstated, ruling that an NFL arbitrator ''failed to meet his duty'' in a child abuse case that shook the league. U.S. District Judge David Doty issued his order Thursday, less than three weeks after hearing oral arguments. Doty overruled NFL arbitrator Harold Henderson's denial of Peterson's appeal. The league suspended Peterson through at least April 15 under its personal conduct policy.