In 1944, he was a batting practicepitcher for the Detroit Tigers. Ideally, the team would have sent him to the minor leagues for experience, but the team could not imagine him folding his long legs on bus rides.[5] He also played for the New York Yankees as well as other farm teams. His baseball career ended after suffering an elbow injury when he was hit by a drive from Rudy York.[6]
Siewert started his professional basketball career with the St. Louis Bombers.[4] Fans started calling Siewert "Timber" because he kept falling like a tree when knocked down by stronger players.[7] In February 1947, the Toronto Huskies acquired Siewert. Siewert averaged just 1.1 points per game with the Huskies and had the lowest field goal percentage on the team.
Siewert scored a total of 20 points in his 21-game career.[4]