He played in Major League Baseball (MLB) as a first baseman from 1925 to 1931 for the Detroit Tigers and the Boston Braves.

Neun is notable for completing the seventh unassisted triple play in MLB history.

Although never an everyday player (he never played more than 97 games a season), Neun entered baseball immortality on May 31, 1927 against the Cleveland Indians, when he caught a line drive from Homer Summa, stepped on first to retire Charlie Jamieson, and despite shouts from his shortstop to throw him the ball, raced towards second base to retire Glenn Myatt, completing the seventh unassisted triple play in MLB history, and the first such play to end a game.

He then spent two seasons as skipper of the Yanks' other top affiliate, the Kansas City Blues of the American Association (where he won another regular-season pennant, in 1942), before joining the New York coaching staff in 1944.

During the offseason, he was hired by the Cincinnati Reds as the successor to Hall of Fame manager Bill McKechnie.