He made his first-class debut in an end-of-season match in the 1938 season as the deputy for Syd Buller, who would later be an umpiring colleague.
Returning to Worcestershire after the Second World War, Yarnold again understudied Buller, who played in 25 of the county's 27 first-class matches.
[3] Buller retired from first-class cricket at the end of the 1946 season, and the following year Yarnold stepped into his position as the regular Worcestershire wicketkeeper.
[4][5] Many of the stumpings, and some catches, were made off the bowling of the unorthodox leg-spinner Roly Jenkins, who took 183 wickets in the season and was named as a Wisden Cricketer of the Year.
He died on the way home from umpiring in a rain-ruined three-day game between Northamptonshire and Essex at Wellingborough when his car crashed into a lorry at Leamington Spa.