The Best Lefthanded Batters and Lefthanded Pitchers in Baseball
From the earliest days of organized baseball, there have been lefthanded pitchers and there have been lefthanded batters. Not in large numbers as there are today, but more proportionate to the number of lefthanders in the general population.
There was no specific effort to include them, and no specific attempt to exclude them. If a lefthanded pitcher could throw strikes and throw hard and throw often, he would be given a chance to pitch. If a lefthanded batter could get on base consistently or hit home runs and drive in runs, he would be given a chance to bat, (as long as he could play either first base or outfield without hurting the team).
By the middle of the 20th century, almost every team had a couple of lefthanders on the roster and people began to pay more attention. Statistical analysis became more advanced and began to show that most lefthanded batters hit better against righthanded pitchers and struggled more against lefthanded pitching, and that most righthanded batters hit better against lefthanded pitchers and struggled more against righthanded pitching.
From the other perspective…the numbers showed that lefthanded pitchers had more success against lefthanded batters than against righthanded batters, and that righthanded pitchers had better success against righthanded batters than against lefthanded batters.
The understanding that most batters fared better against pitchers of the opposite hand changed the game of baseball. Teams began to look for and give more consideration to lefthanded batters, and began to use a platoon system at some positions, where a lefthanded batter would get most of the playing time against righthanded pitchers and a righthanded batter would get most of the playing time against lefthanded pitchers.
Switch-hitters (players who could bat lefthanded or righthanded) also became more prominent. There had always been a few switch-hitters in the game, but now teams looked for switch-hitters in the hope of finding a strategic advantage. Having switch-hitters on the roster gave a team more roster flexibility...if they started they wouldn’t have to be pinch-hit for, and if they were on the bench they could pinch-hit against either a righthanded or a lefthanded pitcher.
During this same time that lefthanded batters were becoming more common, the era of starting pitchers finishing most of their games was also coming to an end, and relief pitchers were also becoming more common. Teams began to look for lefthanded relief pitchers to pitch against lefthanded batters, and the use of lefthanded relief specialists has continued to be a major part of baseball strategy.