As a ninth grader Sims began training with the San Clemente Jets, an amateur wrestling club where kids from all over California came to learn freestyle and Greco-Roman techniques.
In 1996 he quit wrestling in order to work for a computer company but he missed the competition and began to practise again, finishing third at the 1998 U.S. World Team trials.
However, in 1999 while he was training at the U.S. Olympic facilities in Colorado Springs Sims flew his snowboard off a mountainside and had to be transported off the mountain by helicopter.
[3] Sims made his MMA debut at 'Xtreme Pancration 2' in Los Angeles in April, 2002, defeating Steve Bruno by decision.
In total he fought 11 times in his MMA career, including five fights for Pancrase in Japan and took on top fighters of the era such as Koji Oishi, Antonio McKee, Satoru Kitaoka, Yuki Sasaki and Brad Gumm before retiring in 2006 in order to focus on his coaching commitments.