An over-powering right-handed pitcher, Schaefer was drafted by the Los Angeles Dodgers in 1972 after graduating from Lindbergh High School. In 1975, he was drafted by the San Francisco Giants while pitching for the University of Oklahoma at Norman. He played in the Giants farm system for seven years.

He began his minor league career in 1975 with the Great Falls Giants in the Pioneer League. In 1976 and 1977, he pitched for the Fresno Giants in the California League. In 1978, he moved to the Eastern League with the Waterbury Giants in Connecticut. He pitched for the Triple A Phoenix Giants from 1979 to 1981.

In 1972, Schaefer was selected to the Missouri All-State team while pitching for Lindbergh High School. He led Missouri in strikeouts with 102 in 55 innings. He was also named All-Conference and All-Metro in 1972.

Schaefer pitched for the University of Oklahoma Sooners from 1973 to 1975. He played for the Lawton Tigers during the summer of 1973. In the summer of 1974, he pitched for the Kenai
Oilers in Alaska. Schaefer had numerous complete games and played outfield on days when he wasn't pitching.

He coached high school baseball in the St. Louis area from 1981 to 1983.