Deadspin: NBA To Pay $500 Million To Get Out Of The Worst Deal Ever Signed
Basically, when the ABA voted to merge with the NBA, the Kentucky Colonels and Spirits of St. Louis wanted to join as well, but the league did not wish to accept them along with the Nuggets, Pacers, Spurs and Nets. So they bought out those two franchises. The owner of the Colonels accepted $3 million. The owners of the Spirits took $2.2 million...and one-seventh of future television revenue due the four teams that joined.
According to the article, they've already made $300 million off of the deal, which will continue in perpetuity. Now the league is close to a buyout deal for $500 million.