Casey began his professional baseball career with the Atlanta Crackers of the Southern Association, at the age of 18. After going 13–14 for Memphis in 1938, he was drafted by the Dodgers. He pitched effectively for the next four seasons, but his career is best known for an alleged wild pitch that he threw in the ninth inning of Game 4 in the 1941 World Series, which precipitated a Yankee rally. Catcher Mickey Owen thought that the pitch was a spitball; Casey always swore it wasn't. Officially the play was recorded as a passed ball. Brooklyn lost the game and, eventually, the series. Casey went 0–2.