There are nine pitchers in major league history who have had 20-win seasons while splitting time between two leagues, four of them in the 19th Century, four in the 20th Century, and one in the 21st Century.
The four 19th Century pitchers to split time between leagues and win at least 20 games all played in 1884. That year saw the two existing leagues of the time, the National League and the American Association, joined by a rival, the Union Association. The Union Association was founded by a St. Louis businessman named Henry Lucas who tried to entice players to his new league by promising them contracts that didn't have the reserve clause.
The UA lasted just one year, primarily because Lucas had all the good players put on his St. Louis team that won the league with a 94-19 record. The Maroons won 20 straight games to start the season and that was it. Teams came and went during the season and the UA's legacy might be that cities like Altoona and Wilmington can that for at least a few games, they were "major league." Word of advice to future major league cities: Delaware is not a major league state.
Billy Taylor, who had pitched for Pittsburgh of the AA in 1883, joined St. Louis in 1884 and went 25-4 to start the season, before moving over to Philadelphia of the AA where he went 18-12 for a grand total of 43-16. Taylor would win just three more games in the majors.
Charlie Sweeney was a 21-year old pitcher for the Providence Grays of the NL in 1884 and he started out the season going 17-8, but also managed to irritate his teammates, in particular the team's other pitcher Charley "Old Hoss" Radbourn. Eventually, Sweeney was kicked off the team and Radbourn pitched almost every game down the stretch for Providence, winning a major league record 59 games. Providence won the NL flag. Sweeney ended up in St. Louis, pitching for Lucas and went 24-7 for an overall 41-15. Sweeney won just 16 more games in the majors.
Jim McCormick began the 1884 season with Cleveland of the NL and got off to a relatively rough 19-22 start and then jumped over to the UA's Cincinnati Outlaw Reds and went 21-3, for an overall 40-25. The Outlaw Reds were 69-36 and 21 games out of first in either second or third as Milwaukee had a higher winning percentage, but was just 8-4.
Finally, there was Dupee Shaw (ne Fred Shaw), who had a rough go of it with Detroit's NL franchise, at 9-18. Shaw moved over to the Boston Reds of the UA and was a pedestrian (for the era) 21-15 to give him a 30-33 overall record.
Now we flip ahead to 1902 where John McGraw is managing the AL's Baltimore Orioles. One of his best pitchers on his mediocre team was Joe McGinnity. McGinnity was 13-10 midway through the season when McGraw hatched a scheme for him to take over the New York Giants of the NL. McGraw did not like AL president Ban Johnson and wanted to go back to the NL. So McGraw arranged to have some of the best players on Baltimore released and he left Baltimore and took them with him to New York. McGinnity was one such player and he went 8-8 for the Giants. That worked out to an overall record of 21-18. The next year, the Baltimore Orioles would move to New York and bother McGraw even more in their form as the New York Yankees.
In 1904, the Chicago White Sox had a mediocre pitcher named Patsy Flaherty who had gone 11-25 in 1903. Flaherty wasn't used much in 1904 for the White Sox and was just 1-2 in five starts. Then on June 6, the Pittsburgh Pirates purchased Flaherty's contract. And Flaherty put up a sterling 19-9 record with a 2.05 ERA. And that was about it for Flaherty. He went 10-10 in 1905 for the Pirates and after missing the entire 1906 season, the Pirates traded Flaherty to the Boston Braves and he played a bit in the 1907, 1908, 1910, and 1911 seasons. Flaherty pitched one game for the Phillies in 1910.
During World War II, one of the more curious cases of a player switching leagues midseason took place. Hank Borowy had won 48 games for the Yankees from 1942-44 and started off the 1945 season with a 10-5 record, although his ERA had crept up to 3.13 from the 2.60 range it had been. For some reason, Yankee manager Joe McCarthy tired of Borowy and had him put on waivers in July. In what may have been the most astute player transaction in Cubs history, Borowy was picked up off of waivers by Chicago.
In 15 games with the Cubs down the stretch, Borowy went 11-2 with a 2.13 ERA (for a 21-7 overall mark) as the Cubs won the NL pennant by three games over the Cardinals. Borowy won Game 1 of the World Series over the Tigers, 9-0, but lost Game 5. Borowy pitched three innings in relief in Game 6, which the Cubs won 8-7.
To limit travel, the 1945 World Series had the first three games played in Chicago, then then the next three in Detroit with no days off. Game 7 was decided by a coin toss and the Cubs got to be the host and with just one day's rest, Borowy was chosen to start, but he had nothing left. The first three Tiger hitters singled and all would come around to score and the Tigers romped to a 9-3 win to take the Series. That was the last World Series game played at Wrigley Field to date.
Borowy would finish sixth in the MVP voting, which was won by teammate Phil Cavarretta. Borowy would never match his success of the World War II years and never won more than 12 games in a season.
In 1984, Rick Sutcliffe would turn in a Borowy-like performance for the Cubs. Sutcliffe started the season in Cleveland and was just 4-5 with a 5.15 ERA. The Cubs sent Mel Hall, Joe Carter, Don Schulze, and Darryl Banks to Cleveland on June 13, 1984 to acquire Sutcliffe along with George Frazier and Ron Hassey. The Cubs were in first place at the time, but felt they needed another arm to hold off the rest of the NL East.
Sutcliffe made his first start on June 19 in Pittsburgh and the Cubs beat the Pirates beat 4-3. He then shut out the Cardinals 5-0 on June 24, before losing to the Dodgers in Los Angeles on June 29. Sutcliffe then started 17 more games, won 15 of them with two no-decisions and the Cubs lost just one of those games and the Cubs moved on to the postseason as they won the NL East by 6 ½ games over the Mets. Sutcliffe went 20-6 overall.
Like Borowy, Sutcliffe's postseason started off well. The Cubs routed the Padres 13-0 in Game 1 of the NLCS. The Cubs won Game 2 and went to San Diego looking to pick up a ticket to the World Series. But the Padres won Game 3, 7-1, and then took Game 4 in thrilling fashion 7-5 on a walkoff homer by Steve Garvey.
Sutcliffe started Game 5 and the Cubs led 3-2 going to the seventh. Then Carmelo Martinez drew a leadoff walk. Garry Templeton sacrificed him over. Pinch hitter Tim Flannery followed with a sharp grounder to first that Leon Durham let go through his legs and Martinez scored the tying run. Alan Wiggins singled Flannery to second and Tony Gwynn doubled home two runs to make it 5-3 San Diego. Garvey singled home Gwynn to make it 6-3 and Sutcliffe left the game. And the Padres made it to their first World Series. The NL Cy Young Award was Sutcliffe's consolation prize.
The most recent 20-game winner between two leagues happened in 2002. Bartolo Colon had been Cleveland's #1 starter for three seasons and started this season a 10-4 record and 2.55 ERA. However, the Indians didn't think they would be able to afford Colon's increasing salary demands and traded him to Montreal on June 27, 2002. And that deal netted Cleveland Grady Sizemore and Cliff Lee as well as Brandon Phillips and Lee Stevens.
Colon would go 10-4 in Montreal in the second half for a 20-8 overall record and he finished sixth in the NL Cy Young Award voting. Of course, Montreal couldn't afford Colon either and sent him to the White Sox where they got three guys who didn't do much for them in Rocky Biddle, Orlando Hernandez, and Jeff Liefer. The Expos also got cash. They probably liked the cash.