Southworth's managerial career began in 1928 with the Rochester Red Wings of the AA International League (IL), the top club in the Cardinals' farm system. In May, Southworth and his wife experienced the stillbirths of twins. Southworth returned home after losing the twins, but he quickly came back to Rochester. Late in the season, Southworth received word that Billy Jr. had been accidentally shot by a neighbor in Columbus. His son recovered, but the experience shook the manager. The team won the IL championship that season.