Coombs was born on 30 May 1941 in the Victorian town of Swan Hill, to Cecil Coombs and Rosie Clayton. After losing his mother at age five, he and his four siblings lived with relatives in the New South Wales town of Balranald. He grew up in rural Victoria in a large family. He became a paraplegic at the age of 12 when he was accidentally shot in the back while out shooting rabbits. He spent time at the Royal Austin Rehabilitation Hospital in Melbourne where he was introduced to sport as part of his rehabilitation program. One of the sports that he competed in was wheelchair basketball. He competed in the first Australian championships in 1960 and was then selected to compete at the 1960 Summer Paralympics. Coombs only brought one wheelchair to the Paralympic Games, the wheelchair he used every day. His wheelchair weighed about .