De Waal was instrumental in opening up Dutch field hockey to the world. The Dutch had been playing hockey under their own rules, which included a soft ball, flat sticks, mixed teams and no goal circle. This made it impossible to play international games, but with the 1928 Olympics coming to Amsterdam, De Waal decided this had to change. Together with other proponents of the “English” variant of the game, he managed to make the switch and the first international game was played in 1926, against Belgium. The switch worked out great, and De Waal captained the Dutch to a silver medal at the 1928 Olympics, and later a bronze in 1936. After the war, he became head coach of the Dutch national team. At the Helsinki Olympics, he lead his team to another silver medal. He still held that position in 1956, but was unable to go to Melbourne when the Dutch NOC called off the Dutch participation just before their departure, because of the Hungarian Revolt.