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 Professional Billiards Champion from 1951 until 1968, when he was defeated by Rex Williams.
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. He is a member of the New Zealand Sports Hall of Fame