A power-hitting shortstop and third baseman, McDermott was drafted by the Chicago Cubs right after he graduated from high school. From 1970 to 1972, he was the starting shortstop for the University of Missouri at Columbia. In 1972, he led the Big Eight Conference in home runs with six in twenty games. From 1969 to 1974, McDermott played for the Northside Buds in the St. Louis County League. In 1972, he received All-State honors at the NBC tournament. In 1975, he was a shortstop on the American National Insurance team that won the St. Louis County League championship. He was a shortstop and third baseman for Stockham American Legion Post 245, and was named Most Valuable Player in 1967. McDermott played shortstop for Northwest High School in the late 1960s. In 1968, he was named to the All-Public High League team, and received honorable mention on the All-Metro team. In 1968, he also played for St. Adalbert Catholic Church in the CYC League. McDermott coached little league baseball in South St. Louis County for ten years.