But his real breakthrough came in his junior year. KU Coach Bud Moore brought in the wishbone offense and moved Cromwell over to quarterback. It was a bold move that paid off. That year he broke several KU, Big Eight and NCAA records for rushing by a quarterback. Cromwell's speed and agility earned him the nickname, "Ransom Rambler."
He was named the 1975 Big Eight Offensive Player of the Year, rambling for 1,124 yards, which was the third highest in NCAA history at that time.
He was also an honorable mention for All-American honors that year. Cromwell also earned All America honors on the track, setting Kansas records in the 600 and 400 yard runs, the intermediate hurdles and the decathlon.
Going into the pros, he was a second-round draft pick for the Los Angeles Rams. He played safety with the Rams, being named the NFC Defensive Player of the Year in 1980. He also played in the Pro Bowl. He played with the Rams until 1988.