There are 30 teams in Major League Baseball.
These 30 teams are split into two leagues — National and American.
These two leagues are each divided into three divisions — East, Central and West.
MLB teams each play 162-game regular season games to determine six division winners and each of these six teams advances to an eight team playoff.
So where does baseball get the other two teams for the eight team playoff? Well, four additional teams — two each from the National and American Leagues — advance to two “Wildcard” games. To determine the Wildcard teams, divisions are ignored, and the two teams in each league with the overall best records (excluding division winners) earn a one-game playoff to advance to the next round.
As The New York Times notes, a one-game playoff is not the norm in MLB:
For all of baseball history, postseason series had been decided by multiple-game playoffs, often five or seven games, testing an entire pitching staff and allowing teams a chance to come back after a poor game or two. Now teams, including those with 90 wins or more, would face off in a life-or-death game.
MLB’s logic for this is pretty simple. An eight-team playoff works, but it doesn’t fit well with each league being divided into three divisions. Why not change the number of divisions? Well, three — or six in total — works better over the course of a full season because it creates a lot more excitement as teams battle for a lot more division titles. It also creates excitement when four teams are battling in do-or-die games.
In the end, the behemoth of Major League Baseball can do whatever it wants, but it’s still a little nutty for a team to grind through 162 games and then have their playoff hopes reduced to just one game.