He played for the St. Louis Bombers and Toronto Huskies during the inaugural 1946–47 season of the Basketball Association of America.

[3][4] At high school in Mount Clemens, Michigan, Siewart was both a center in basketball and a first baseman in baseball.

His baseball career ended after suffering an elbow injury when he was hit by a drive from Rudy York.

[4] Fans started calling Siewert "Timber" because he kept falling like a tree when knocked down by stronger players.

Siewert averaged just 1.1 points per game with the Huskies and had the lowest field goal percentage on the team.