Armstrong represented New Zealand in field hockey from 1950 to 1962,[2] including at the 1956 Olympic Games in Melbourne.[4] He went on to coach the New Zealand field hockey side at the 1968 Olympics in Mexico City, and the Auckland provincial team from 1971 to 1984.[2] He was also a tennis umpire, and officiated at Wimbledon.[2]
He was the principal of Mangere College from its foundation in 1971 until 1988; it was the first school in New Zealand not to use corporal punishment.[2] He married Joan and they had three children.[2]
