According to Ohio State, Cassady died early Friday morning in Tampa, Florida.
Cassady starred as a halfback for the Buckeyes from 1952 to 1955 and won the Heisman as a senior by the largest margin at that time. He was inducted into the College Football Hall of Fame in 1979 and is also enshrined in the Ohio State Athletics and Columbus (Ohio) Baseball halls of fame.
"We've lost not only a legendary Buckeye, but also a wonderful person in Hop Cassady," Ohio State athletic director Gene Smith said in a statement. "He was an all-time great Buckeye in every way. We will have the Cassady family in our thoughts and in our prayers."
His coach, Ohio State legend Woody Hayes, described Cassady as "the most inspirational player I've ever seen."
Cassady departed Ohio State as the school's career leader in rushing yardage, all-purpose yardage and scoring. He played nine professional seasons, including seven with the Detroit Lions, primarily as a defensive back and won an NFL championship in 1957.
He also played baseball for the Buckeyes and followed his NFL career with more than 30 years of service in the Yankees organization. Cassady met George Steinbrenner, the Yankees' longtime owner and a fellow Ohioan, through their association with the U.S. Air Force.
Steinbrenner hired Cassady in 1976 as the team's conditioning coach, preceding World Series championships for the club in 1977 and 1978. Cassady later worked as a Yankees scout and special instructor and as a coach for New York's Triple-A affiliate in Cassady's native Columbus.
Cassady and his wife, Barbara, retired near Tampa, the Yankees' spring training home.
At Ohio State, Cassady vaulted to stardom in 1952, coming off the bench to score three touchdowns against Indiana. The freshman performance helped earn him the "Hopalong" nickname from Ohio sportswriters, a reference to fictional performing cowboy Hopalong Cassidy, played on film by Ohioan William Boyd.
Cassady scored 37 touchdowns in 36 games with the Buckeyes and was named an All-American in 1954 and 1955. He finished third in the Heisman voting as a junior, helping lead Ohio State to Hayes' first national title with a Rose Bowl win over USC.
Ohio State retired Cassady's No. 40 jersey in 2000, displaying it at Ohio Stadium alongside fellow Heisman winners Vic Janowicz and Archie Griffin.
At the time, Cassady said he never saw himself as a star.
"I just lived from day to day," he once told OhioStateBuckeyes.com. "Back then, there were no scholarships, so I worked, played ball and went to school."