Rube Waddell
Rube Waddell was one of the greatest pitchers ever to take the mound at his peak, but other struggles prevented him from reaching his full potential as one of the greatest few pitchers to ever live.
In the first 5 years of his career, he played for 7 teams, including 4 minor league teams, because he quickly wore out his welcome everywhere he went. He was known to sneak off in the middle of a game to go fishing, or to leave the field to chase a passing fire truck. He was also a raging alcoholic, and it is said that he spent his entire first signing bonus on alcohol.
In 1902, he was picked up by the Philadelphia Athletics, where manager Connie Mack was able to keep him somewhat under control for a few years, and the following 6 years were some of the most productive any pitcher has ever had.
He led the league in strikeouts for 6 consecutive seasons, and topped 300 strikeouts in 1903 and 1904, a feat no other pitcher would reach in consecutive seasons until Sandy Koufax in 1965 and 1966. Not only did he have a huge number of strikeouts, but he led the league by an enormous margin each time, with no pitcher coming within 100 strikeouts of him in either of those seasons.
The next season he dropped to 287 strikeouts, but he accomplished another major feat when he won the pitching Triple Crown, topping the league with a 1.48 ERA and 27 wins as well as the usual strikeouts. His team reached the World Series that year, but he didn't pitch, and there is some controversy as to the reason, as he and the team claimed a shoulder injury, but had conflicting stories as to what happened. There is also a rumor that he was paid by a gambler to skip the Series, but that has not been proven.
After the 1907 season, despite still being the league's top pitcher, the A's grew tired of his antics and sold him to the Saint Louis Browns, where his performance regressed quickly, and by the end of 1910 he was out of the majors completely. He died of tuberculosis just a few years later, leaving behind a strange and amazing legacy.
It is unclear what caused Waddell's bizarre behavior, and it's unfortunate that there was no help available to him for his possible mental health disorder, because he was one of the most talented pitchers to ever take the mound, but even in his abbreviated career, he showed enough greatness to be included on this list of the all-time greats.