Twellman played second base in the Houston Astros farm system from 1974 to 1976. He played in Iowa for the Cedar Rapids Astros and the Dubuque Astros before joining the Double A Columbus Astros in Columbus, Georgia. Twellman was an All-Metro second baseman at St. Louis University High School. He also starred in football and soccer at St. Louis University High School. He was the starting second baseman at SIU-Edwardsville from 1971 to 1974. He was the leading hitter on his team in 1973 with a .352 average. That year, the Cougar baseball team captured third place in the NCAA national tournament. In 1974, he led his team in hitting with a .367 average while striking out only once in 156 times at bat. He was captain of his team. Twellman was named an All-American in both baseball and soccer at SIU-Edwardsville. In 1972, he helped the Cougar soccer team win the national college division championship. He was twice named The Most Valuable Athlete at SIU-Edwardsville. In 2007, Twellman was inducted into the SIU-Edwardsville Athletics Hall of Fame as an individual for baseball and soccer, and as a member of three different championship teams. Twellman played second base for two years with the Springfield Capitals in the Central Illinois Collegiate League. He played in the St. Louis County Senior League for the Geigher Collegians and the Kutis Collegians. Twellman coached parish baseball for his church for ten years. He served as parish athletic director for six years. He also coached three other amateur baseball teams for over ten years.