Cahill is a Judo Professor and a South San Francisco High alumnus. He has been teaching and coaching Judo and Jujitsu for the better part of five decades. His pupils have captured more than 1200 national and international titles. A former judo coach at Stanford and San Francisco State Universities, Cahill was the U.S. Olympic Judo assistant Coach at 1984 Summer Olympics in Los Angeles and at 1988 Summer Olympics in Seoul. He was offered a U.S. Olympic Judo Head Coach position for the 1992 Summer Olympics in Barcelona, but passed the opportunity, as he thought there were better candidates. He also coached the U.S. National Judo team from 1980 to 1990. Cahill became a Northern CA Youth Champion at the age of 16. As a coach, his San Bruno Judo Academy won nine straight California championships in the 1970's. Willy's teams competed in the Olympics, Goodwill Games, World Judo Championships, the Pacific Rim Championships and the Junior Pan American Championships. Professor Cahill mentored and trained athletes such as a 1987 World Judo Championships Silver medalist Lynn Roethke, a 1984 Olympian Brett Barron, a 1984 Olympic Bronze medalist Edward Liddie and a Silver medalist Robert Berland, a 1988 Olympic Silver medalist Kevin Asano and a Bronze medalist and a 1987 World Champion Mike Swain. One of Cahill's students, Corinne Shigemoto, has been named a U.S. Olympic Judo coach.