As well as being a rugby union player, Williams was also a successful tennis player at youth level, before fully committing to rugby. He won the 1966 British Junior title at the All England Lawn Tennis and Croquet Club in Wimbledon, beating David Lloyd 6–4, 6–4; this is often erroneously cited as being a Junior Wimbledon victory, including in J.P.R.'s autobiography, when in fact it was won by Vladimir Korotkov.
