Shields began amateur wrestling at age nine. He has competed in over 601 folk, freestyle, and submission wrestling matches. Shields was a four-year varsity wrestler and state qualifier at Calaveras High School, finished 2nd place at the Amateur Athletic Union National Freestyle Championships, qualified for U.S.A./ FILA Nationals & World Team Trials in both the junior & university men's divisions. He is also a two-time junior college All-American wrestler from Cuesta College, placing 4th in the California JC state tournament in the 177 lb weight class in 1997 and 3rd in the 197 lb weight class a year later. In September 1999, Shields began his MMA training by joining Chuck Liddell's SLO Kickboxing Academy. Within a few weeks he fought his first fight, filling in for an injured teammate at 185 lbs. Shields fought five fights at 185 lbs "for fun, to stay in shape and learn some self defense". In 2001, Shields decided he wanted to make a career of mixed martial arts and began fighting at his natural weight of 170 lbs (77 kg).