Riley was the starting quarterback and punt returner for most of the 1927 season at the University of Notre Dame. He is mostly remembered for his last game with the team—a controversial 7–6 victory at USC before the largest crowd ever to witness a football game at that time (estimated to be 120,000 in attendance).
While clinging to the one-point lead late in the game, Riley fielded a USC punt at his own goal line and appeared to fumble it out of the end zone, which would have given the Trojans a safety and an 8–7 lead. But the play was ruled a muff, and therefore a touchback. Notre Dame would hang on for the win.
In 1930, Riley was hired by fellow Notre Dame alum Tom Lieb to be his assistant football coach at Loyola Los Angeles. One year later, Riley became the head football coach for the University of New Mexico and remained there for three years, but posted a disappointing record of 7–13–3. He died on July 19, 1971.