He first played for Glamorgan as a fast bowler in 1920, the year before they achieved first-class status, but switched to off-spin after some back trouble.

[3] He played for the club till 1949, as captain from 1924 to 1927 and then again in 1929 and 1946, when they finished sixth, their best position to that time, and at the age of 48 he took 120 wickets at an average of 12.72.

In 1935 Clay was called up to play a Test match for England at the Oval against South Africa, but did not take a wicket and did not bat.

[7] In 1929 he made his only Championship hundred against Worcestershire at Swansea, batting at number 10; his stand of 203 with Joe Hills for the ninth wicket is still the club record.

[1] John Arlott thought Clay was the best off-spin bowler in England: "Some others, perhaps, spun the ball harder – though not markedly so – but no-one until Laker of a later generation combined his degree of spin and such accuracy, subtlety, and variety of flight.

He served as secretary of the Glamorgan Hunt, and steward and director of Chepstow Racecourse, which had been laid out in the grounds of his family home at Piercefield Park in the 1920s.