The A.B.L. was a single-entity structure under which all teams were centrally owned and the players were signed and paid by the league.

MLS operates under a single-entity structure in which teams are centrally owned by the league.

The league won a bitter legal battle with its players over its economic system, which was eventually resolved with the players gaining some improved benefits in return for accepting the single-entity structure.

Currently, there is little enticement for M.L.S. clubs to do this, he said, because player contracts are owned by the league, not by individual teams, in a so-called single-entity structure.

But last November, the N.B.A. Board of Governors voted to change the W.N.B.A. business model from a single-entity structure to individual team ownership.

The league operated as a single-entity structure, with practically all operations handled out of headquarters in Palo Alto, California.

The single-entity structure is used by the Women's N.B.A. and Major League Soccer, which has team investors but is centrally controlled.

The six surviving teams organized the MISL as a single-entity structure similar to Major League Soccer.

Clearly, though, the league's single-entity structure is intended to control marketing and costs, and that desire to control costs has produced strikingly restrictive contracts with the players.

The league's single-entity structure is aimed at, among other things, limiting financial disparities between teams in large and small markets.