At the 1928 Olympics in Amsterdam, Netherlands, Clapp won a gold medal as a member of the winning U.S. team in the men's 4×200-meter freestyle relay, together with Walter Laufer, George Kojac and Johnny Weissmuller. The Americans set a new world record of 9:36.2 in the relay event. Individually, he placed fifth overall in the men's 400-meter freestyle and also competed in the preliminary heats of the men's 1,500-meter freestyle.