The N.B.A. has long hoped to be released from its financial obligation to Ozzie and Daniel Silna, brothers who owned the Spirits of St. Louis in the defunct American Basketball Association.

But it has never been easy. The Spirits were excluded from the 1976 merger of the two leagues. So the Silnas watched unhappily as the New York (now Brooklyn) Nets, the Denver Nuggets, the Indiana Pacers and the San Antonio Spurs were absorbed into the N.B.A. But the Silnas negotiated an astonishing benefit that was critical to the merger: an agreement to be paid one-seventh of the national television revenue that each of the four teams was to receive, as long as the league continued to exist. That amounted to being paid in perpetuity, and so far, the deal has provided the Silnas with about $300 million.

Their deal is as much a part of A.B.A. history as red, white and blue basketballs, the 3-point line and the big Afros of Julius Erving and Darnell Hillman. It is a lasting memory of how, through luck or prescience, the Silnas and their lawyer, Donald Schupak, capitalized on the league’s growing popularity.

The N.B.A. has tried to buy them out, including an effort before the financial crash in 2008. Negotiations have picked up in the last six to nine months.