As a player, Prothro was discovered by baseball promoter Joe Engel, who managed the
Chattanooga Lookouts at
Engel Stadium. In 1928, Prothro became a manager in the
Southern Association (SA), then one of the higher-level minor leagues, leading the
Memphis Chicks and
Little Rock Travelers to four SA pennants through 1938. In 1939, Prothro replaced
Jimmie Wilson as manager of the
Philadelphia Phillies. In his three full seasons (1939–1941) at the helm of the Phillies, the club remained locked in the
National League cellar — losers of 106, 103 and 111 games. Prothro's career mark of 138–320 has the lowest managerial
winning percentage, .301, in major league history. Prothro was fired after the 1941 season and replaced by
Hans Lobert and thereafter returned to the Southern Association, where he piloted the Chicks from 1942 to 1947. After he retired as Memphis' manager, he remained active as a co-owner of the club. ==Personal life==