He was the starting second baseman for St. Louis University from 1971 to 1974. During those four years, his On Base Percentage was .380 and his Fielding Percentage was .962. In 1971, he batted .333 as a freshman. In 1972, he only committed one error as a sophomore. He had a perfect Stolen Base Percentage while playing for the Billikens. In 1974, he stole 21 bases out of 21 attempts. That year, he was the co-captain of his team. He received a four-year scholarship to St. Louis University for baseball and basketball. McDermott set career records at St. Louis University for Most At Bats, Most Runs, Most Walks, and Most Games. From 1971 to 1974, he also played during the summer for the St. Louis University Club team. His batting average was over .300 each year. In 1973, his average was .378. He was selected to the St. Louis County League all-star team in 1972 and 1974. McDermott lettered all four years in varsity baseball at Northwest High School, playing from 1967 to 1970. In 1970, he was selected as an All-Public High League Shortstop, and he received honorable mention as an All-Metro Shortstop. That same year, he was the Post-Dispatch scholar-athlete for Northwest High School. He received his award from Stan Musial at the scholar-athlete banquet. In the late 1960s, McDermott was the starting second baseman for the Stockham Post 245 American Legion team. In 1975, he was the starting second baseman for the American National Insurance team that won the St. Louis County League championship. The following year, he was the player-manager of the team, guiding American National to a second-place finish in the St. Louis County League playoffs. McDermott was the manager of youth baseball teams in the Bridgeton Athletic Association and the Ballwin Athletic Association.