Arnold, who rushed 104 yards for Arkansas State (2-4, 1-2 Sun Belt), scored on a 14-yard run with 6:08 left. His TD was set up when teammate M.D. Jennings recovered a Florida International (1-6, 1-3) fumble on the previous play.
Leonard rushed for a career-high 120 yards and tossed a 5-yard touchdown pass to Jeff Blake. The Red Wolves also scored on a 5-yard run by Derek Lawson. Josh Arauco added field goals of 26 and 32 yards.
FIU scored on a 36-yard field goal by Dustin Rivest and a 2-yard run by Darriet Perry.