At Mark Keppel High School of Alhambra in Los Angeles County, Marshall was a team captain who earned the Most Valuable Wrestler award, coached by Dave Long, Dick Knowles and Jim Hold, 1965-69. Playing football led him to wrestling, and his success on the field was largely due to the experience he gained on the wrestling mat. While wrestling at Mt. San Antonio College under coaches Fred Burri and Robert Combs, Thompson placed 6th in the California Junior College State Championships. He also earned the Most Inspirational Wrestler Award there, and he compiled a record of 113-44-3 over his high school, JC, AAU and other tournaments. Marshall began coaching while earning his BA from BYU and a Master's Degree from California State University - Long Beach. In his 40 years as a high school wrestling coach (37 years as Head Coach), he served at: Millard HS in Fillmore, UT (1975), Snowflake HS in Snowflake, AZ (1976-77), Millikan HS in Long Beach, CA (1977-78), Wilson HS in Long Beach (1978-80), Mark Keppel HS (1980-91), East LA College in Monterey Park, CA (1990) and back at Millikan (since 1991 and currently). Thompson's overall varsity dual match record of 811-252-6 includes six CIF Championships in 1987, 2003, 2004, 2010, 2015 and 2016. His teams won 26 League Championships, with 216 individual League Champions, 27 CIF-SS Divisional Champions, 152 CIF Placers, 42 State Qualifiers, and 11 State Medalists including three girls. Marshall has always worked hard to put a competitive team on the mat every year while encouraging participation from all students -- regardless of skill or potential. In recognition of his efforts and success, Marshall has been selected as League Coach of the Year 21 times. He has been recognized as the Dream Team Coach of the Year by the Long Beach Press-Telegram in 2003 and 2010, and he also received the Long Beach Century Club's High School Coach of the Year Award in 1999 and their Outstanding Leadership to Youth Award in 2009. Marshall helped to manage 16 wrestling tournaments for the LA Watts Summer Games, and they gave him their Sportsmanship Award in 2008. He started the Moore League's first girl's wrestling team in 2012, and he has been the tournament manager of 98 wrestling tournaments. He has been involved with USA Wrestling, Ram Wrestling Kids Club, the Moore League, Millikan Coaches Iron Man Club, and the Boy Scouts.