Such FACs would organize and collect money (pledged conditionally via credit card) from other fans to provide a one-time (or perhaps even a recurring) payment for a player who joins or stays with the team. The organizers of the FAC could track the number of fans participating, as well as the money raised, as a demonstration of fan love for the player. In essence, FAC members operate like college boosters, showing their support for their teams through money. The difference is that the money goes not to the team, but to the players.
One objection to this idea might center on the collective bargaining agreement between the league and its players. That agreement limits the amount of money a player can make -- depending on service time in the league and roster slot -- and prohibits teams from compensating players in any way other than basic salary. It also holds down the total salaries a team can pay by imposing a luxury tax on teams that exceed the salary cap.
But the CBA controls only what teams can pay players. It does not limit the money players can make or receive from other lawful sources, such as endorsements or gifts. So long as teams do not coordinate or work with the FACs, the CBA is irrelevant. Like endorsement deals, the money from fan committees would simply provide the player another form of outside compensation.
A second concern would be the relationship between the player and the FAC. A player cannot be an employee of the FAC, since fans do not want to be employers and thereby endure all the legal consequences that go with that. Players and FACs could avoid this problem if the money is donated to a charity of which the player is known to be fond. Although it's not a direct financial incentive, it still benefits the player and expresses the fans' affection. A charitable contribution also does not look quite as absurd as a group of billionaires or working-class fans scraping together money for a player already earning millions a year from his team. The charitable donation approach would further address a likely NBA concern for players having financial relationships with possibly undesirable people and being subject to their undue influence. Having the money go to charity breaks any suspicion of an ugly quid pro quo between player and fan.
A final concern has to do with the main goal of the system of salary caps and luxury taxes: competitive balance. Arguably, a FAC associated with a large-city team player based could collect more money and supporters than a similar one in Indianapolis or Sacramento. It would seem the rich would only get richer when it comes to signing players. But large cities already enjoy advantages in attracting players, primarily in greater endorsement opportunities. And these cities would still have to compete with the attractions of small cities: less traffic and perhaps more communal solidarity, among other factors. Thus, the size and power of a FAC in a given market is simply another aspect of that city's attractiveness to athletes. And support for teams and their star players is not restricted to the cities in which the teams reside.