Nate Bain barreled down the length of the court with seconds left in overtime, made a layup at the buzzer and clinched one of the most improbable upsets in the history of college basketball: Stephen F. Austin beat No. 1 Duke.

Ryan Ivey, the school’s athletic director, was sitting behind the visitors’ bench in Cameron Indoor Stadium and had a perfect view of Bain’s game-winner. But in the delirious aftermath of Stephen F. Austin’s incredible win—a huge underdog from a mid-major conference slaying the top-ranked team in the...