There were two Pitchers in baseball who were named Dutch Leonard.  The first was Hubert “Dutch” Leonard, who was a lefthander who had a 139-113 record with two World Series Championships with the Boston Red Sox.  The second was Emil John “Dutch” Leonard, a righthander who may not have had a World Series Ring, but had a much longer tenure and was one of the better knuckleballers in baseball history.

Leonard debuted in 1933 with the Brooklyn Dodgers, and while he had a decent 1934 (14-11, 3.28 ERA), he faltered and was back in the minors by 1936.  The minors allowed him to perfect his knuckleball, and he was back in the Majors, this time with the Washington Senators, with whom he returned in 1938.

With the Senators, Leonard secured a 20 Win season (1939) and would go to three All-Star Games.  He was in the top ten in bWAR for Pitchers and ERA four times with Washington.  The knuckleballer was also first in WHIP (1938), and twice in BB/9 (1938 & 1943) as a Senator.

As is typical with many who mastered the knuckleball, Leonard played into his 40s.  He was with Philadelphia for two years, and at the age of 40, he joined the Chicago Cubs, where he played five more seasons, including an All-Star season in 1951.

Leonard had 191 Wins against 181 Losses over his career.

Hubert "Dutch" Leonard arrived in Boston in 1913 and immediately established himself as a left-handed force. Following a stellar rookie campaign, he authored a sophomore season in 1914 that defies modern comprehension. Leonard went 19–5 and set a Major League record with a 0.96 ERA—a mark that remains the lowest in the live-ball or deadball era for any pitcher with at least 200 innings paired that microscopic ERA with league-leading marks in FIP (1.95), WHIP (0.886), and Strikeouts per 9 (7.1).

Leonard was the engine behind the 1915 and 1916 World Series titles. While the Red Sox rotation was deep, Leonard was their postseason "Closer" before the role existed. He was a collective 2–0 with a 1.00 ERA in Fall Classic play, including a brilliant performance in 1915, where he helped dismantle the Phillies. His ability to maintain a 2.13 career ERA in Boston during a stretch when he faced some of the greatest contact hitters in history marks him as a premier talent.

His story is one of peak brilliance followed by the era's typical roster churn. Before his famous feud with Ty Cobb in Detroit or his move to the Yankees, Leonard was the left-handed anchor of Fenway Park. He threw two no-hitters in a Red Sox uniform, one in 1916 and another in 1918, joining an elite tier of "hurlers who possessed the ‘swing-and-miss' stuff necessary to dominate without the help of his defense.

Leonard left Boston with a 90–64 record and 771 strikeouts. Though his tenure was shorter than some of the "Lifers" in the Lab, his concentration of excellence was so high that he was finally inducted into the Red Sox Hall of Fame in 2012.

After four nondescript years in Brooklyn, Dutch Leonard arrived in the nation’s capital in 1938, bringing a fluttery, unpredictable knuckleball that haunted the nightmares of the league’s greatest hitters. While many who threw the "knuckler" struggled with its erratic nature, Leonard mastered the pitch with a surgical precision that defied the laws of physics.

Leonard’s tenure was marked by exceptional mastery of the strike zone, uncommon for a knuckleballer. He exemplified efficient pitching, leading the American League in BB/9 twice (1939, 1945). His peak was in 1944 when he led in WHIP (1.114). His restraint was best shown in 1945, when he led the AL in Strikeout-to-Walk ratio (2.41), impressive for a pitcher who rarely struck out many but refused to give free passes.

Leonard earned a reputation as a big-game craftsman, with three All-Star selections (1940, 1941, 1943) during his Washington career. Jackie Robinson praised his knuckleball as one of the most difficult pitches to handle, highlighting Leonard's ability to generate movement while pinpointing location. He was a key part of the 1945 staff that fell just one game short of a pennant.

Dutch Leonard’s tenure in Washington ended abruptly after the 1946 season. Despite being a key rotation player, a contract and role dispute led to his trade to the Phillies for infielder Merrill May in December 1946.

With the Senators, Leonard had a record of 118-101 with a 3.27 ERA.