Duff commented that his most distinguished feat on the cricket field was that in his first year in the XI at Radley, he drove Sir George (Gubby) Allen to retirement in 1954.

Duff made his first-class debut in June 1959 for Oxford University against Essex, and had a decent game in a heavy defeat, scoring 53 and 4 with the bat and taking three wickets (the first of these being that of Gordon Barker).

He played for the university for the first half of the season, then in July and early August appeared in four County Championship games for Worcestershire; in one of these, again against Nottinghamshire, he hit an unbeaten 50.

As a club cricketer he was a member of and played for the Free Foresters, IZ, Arabs, Cryptics, Gentlemen of Worcestershire, Sussex Martlets and Radley Rangers.

While in Barbados he spotted a young Ricardo Ellcock, aged 14, eventually arranging a place for him at Malvern College and helping to launch his first class cricket career.

During his teaching career Duff also contributed to the development of the Nuffield Science Project working with John Lewis and was awarded a prize for Outstanding Teachers by the Institute of Physics in 1988.