His endurance and longevity as a sportsman was astonishing. He was the New Zealand professional billiards champion from 1914 until 1980. He also held the title of World billiards champion from 1951 until 1968, when he was defeated by Rex Williams.
He reached the final of the World Snooker Championship in 1932 and 1952 but never won it.
Clark was a keen advocate of physical fitness and regularly ran up to four miles every day. A strict teetotaller and non-smoker; he attributed his continued success well into his senior years to these things. He was also well-known for walking around the table on his hands before the match started.