Chaplin is retired from Washington State University. Before beginning his tenure at Washington State, which extended 27 years, he coached at Wapato High School in both track & field and cross country.

One of the many Olympians he coached is former world record holder, Henry Rono. At Washington, Chaplin was named District Coach of the Year eight times; he is chair of the USATF men's track & field committee and was the 2000 men's Olympic Track & Field Head Coach.