When the NBA was formed via merger in 1949, eight of nine NBL teams entered the new NBA. The ninth, the all-Black, Black-owned Dayton Rens, was excluded. After inheriting the NBL’s worst record midseason, the Rens had a playoff-caliber mark, but the NBA cited the inherited record to disqualify them
To clarify (ran out of characters), the Rens took on the worst team’s record midseason, which was 2-17. In other words, they were 2-17 before actually playing a game. The NBA’s first commissioner, Maurice Podoloff, and the NBL, cited that they had the worst record in the league, and used that justification to exclude them.
They only had the worst record because they inherited that other team’s record (in a 59 game season), and in the games in which they played they had a winning percentage good enough to make the playoffs.
This was despite half of their team having to leave to barnstorm due to a lack of financial support in what, at the time, was a deeply racist and segregated city in Dayton, Ohio. An estimated 1⁄5 of Daytonians at that time were a part of the KKK.
For the league’s first season, instead of having an all-Black team, there were no Black players in the league. The Rens were arguably the best team in history up to that point, at one point winning 88 straight games and multiple world championships, but were repeatedly undercut by corruption, possibly rigged games, refusing to play into stereotypes of the time period, and Podoloff, who the MVP trophy was named after until 2022. A confluence of these factors forced them to dissolve within the next two years.
If you’re interested in background on the situation, as well as a very different early history of the Harlem Globetrotters than what is often portrayed, here’s a much more detailed post: https://np.reddit.com/r/nba/comments/1u945h0/oc_the_new_yorkdayton_renaissance_the_littleknown/