DeBeers, the diamond behemoth, limited supply of and fixed prices on sparklies for years and years and in all 50 states plus the District of Columbia.  But it sold to only a small group of outfits, none of which dared sue the font of their mercantile wealth.

That didn't stop indirect purchasers from bringing cases

Plaintiffs who sue under section 1 of the Sherman Act must allege a contract, combination, or conspiracy that restrains competition.  Some kinds of conspiracies so patently harm competition that courts presume injury and call them "per se" violations.  Agreements between competitors to fix prices, not to compete for specific customers or in particular areas, and to boycott