Prothro was so nicknamed because he was a practicing dentist before signing his first professional baseball contract at age 26.

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.

[3][a] 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.

His son, Tommy Prothro, became a successful coach in college football (at Oregon State University and UCLA) and, during the 1970s, led the Los Angeles Rams and San Diego Chargers of the National Football League.