Irving Darius Hadley (July 5, 1904 – February 15, 1963) was an American Major League Baseball pitcher. Born in Lynn, Massachusetts, he played the major leagues for the Washington Senators (1926–31 and 1935), Chicago White Sox (1932), St. Louis Browns (1932–34), New York Yankees (1936–40), New York Giants (1941), and Philadelphia Athletics (1941).

He helped the Yankees win the World Series every season from 1936 to 1939.

He led the AL in Hits Allowed/9IP in 1930 (8.37) and 1931 (7.26); Strikeouts/9IP (6.21) and Games (55) in 1931; Innings (316 ⅔) and Batters Faced (1,365) in 1933 and Win-Loss percentage (.778) in 1936.

In 12 seasons he had a 161–165 Win-Loss record, 528 Games (355 Started), 135 Complete Games, 14 Shutouts, 108 Games Finished, 25 Saves, 2,945 ⅔ Innings Pitched, 2,980 Hits Allowed, 1,609 Runs Allowed, 1,389 Earned Runs Allowed, 167 Home Runs Allowed, 1,442 Walks, 1,318 Strikeouts, 66 Hit Batsmen, 71 Wild Pitches, 13,034 Batters Faced, 5 Balks, a 4.24 ERA and a 1.501 WHIP.

On May 25, 1937, Hadley, upset by a home run in a previous at bat, threw the pitch which hit Mickey Cochrane in the head. The resulting injury nearly killed Cochrane, and ended his playing career.