After entering pro ball in the Class D Texas Association as a 21-year-old in 1926 with the Temple Surgeons, Caldwell made his MLB debut with the Philadelphia Phillies on September 8, 1928, and pitched a 4–0, six-hit shutout over the Boston Braves, but lost four games after that, and was let go at the end of the season.
After playing in Class D Texas Association baseball at age 21 with the Temple Surgeons, Caldwell made his Major League debut for the Philadelphia Phillies on September 8, 1928, pitching a shutout against the Boston Braves but lost four games after that and was released from the team.