P owns and operates three integrated beef-packing plants. These markets are highly competitive, and the profit margins of the major beef packers are low. The current markets are a product of two decades of intense competition, during which time packers with modern integrated plants have gradually displaced packers with separate slaughter and fabrication plants. P is the country's fifth-largest beef packer. D is the second-largest packer. D operates five integrated plants and one fabrication plant. D signed an agreement to acquire the third-largest packer in the market, Spencer Beef. Spencer Beef owned two integrated plants and one slaughtering plant. D would still be the second-largest packer, but would command a market share almost equal to that of the largest packer, IBP, Inc. P brought an action under §16 of the Clayton Act alleging that the acquisition would '[violate] Section 7 of the Clayton Act because the effect of the proposed acquisition may be substantially to lessen competition or tend to create a monopoly in several different ways; the proposed acquisition will result in a concentration of economic power in the relevant markets and threaten P’s supply of cattle. The district court eventually granted the injunction. The court held that P's allegation of 'price-cost 'squeeze'' that would 'severely [narrow]' P's profit margins constituted an allegation of antitrust injury.
On appeal, D argued that an allegation of lost profits due to a 'price-cost squeeze' was nothing more than an allegation of losses due to vigorous competition, and that losses from competition do not constitute antitrust injury. The Court of Appeals held that the District Court's decision was not clearly erroneous. The Supreme Court granted certiorari,