An outstanding right-handed pitcher, Dennis was offered a professional contract after his freshman year at St. Louis University. He played for the Billikens from 1967-71, was named Athlete of the Year in baseball in 1971, and became the pitching coach for them in 1974. From 1967 to 1979, Hauswirth pitched for several teams, winning multiple St. Louis County League championships.

He was the head baseball coach at Linn Technical College from 1975-79 and was named All-Regional Coach of the Year his final season there.