Larry Kelley, the 1936 winner from Yale, played on defense during his college days but was much better known for his pass receiving ability. Leon Hart, the 1948 winner from Notre Dame, also played on both sides. The only player that was strictly a defensive player that won the Heisman was cornerback Charles Woodson, the 1997 winner from Michigan. Click on the 'Heisman Trophy Winners' link on this page to view all of the winners starting from 1935.
Actually Woodson wasn't the just a defensive player he won the award mainly because of his punt and kick returning granted he was a great corner but that wasn't enough for him to win the fact he was a great return man gave him the heisman