His junior college football prowess in his early 20s led him to the attention of University of Idaho head coach Dixie Howell, a hall of fame player in the 1930s from Alabama, who was tipped off by a friend. Riley, at 5 ft 10 in and 155 lb , informed Howell he was significantly larger than he actually was, which earned him an invitation to campus.
Upon his arrival in Moscow in 1948, Howell wanted the undersized Riley run off; though he had an assistant coach place Riley in a post-practice tackling drill with a much larger player, Riley prevailed and stayed on the team.
He played halfback for the Vandals in the Pacific Coast Conference from 1948 to 1950 under Howell. In the home opener against Oregon in 1948, Riley scored the Vandals' only touchdown in a 15–8 loss in his first game at Neale Stadium. The 1948 Webfoots featured Norm Van Brocklin and John McKay,and finished the regular season at 9–1 as PCC co-champions. Riley also played for the Vandals' baseball team.
In May 1962, he moved up to the collegiate coaching ranks and joined the coaching staff at his alma mater, the University of Idaho, under first-year head coach Dee Andros. The Vandals posted their first winning record in a quarter century in 1963, and in 1964 they beat neighbor WSU for the first time in a decade and barely lost the week before at Rose Bowl-bound Oregon State 10–7 on a second half punt return.
Riley then moved to the Canadian Football League (CFL) in 1973, as defensive coordinator of the Saskatchewan Roughriders, where he made significant improvements to a poorly rated defense. Riley was hired as the head coach of the Winnipeg Blue Bombers in 1974; head coach Jim Spavital was fired after the Blue Bombers finished last in the Western Conference in 1973.
Riley spent the 1984 season as defensive coordinator for the Edmonton Eskimos. He moved to the front office in 1985, serving as the Calgary Stampeders player personnel director for three seasons. He also served as interim coach for the remainder of the 1985 season after the firing of head coach Steve Buratto.