An assistant principal subdued a student gunman who shot his principal at a South Dakota high school on Wednesday. No students were injured, authorities said. An armed 16-year-old student, whose name has not been released, walked into Principal Kevin Lein's office just before 10 a.m. and a struggle ensued. The gun went off and Lein was hit in the arm with a bullet. Assistant Principal Ryan Rolling heard the shot and tackled the shooter, according to Sam Clemens, Sioux Falls Police information officer. Officials said a motive is still unclear, but the teen's father told the AP his son had been quiet over the past year and thought he was "just mad at everybody." The principal was treated at a hospital and was home recovering after the incident.