Columbia Outdoor (D) entered the billboard business in the city of Columbia (D) in the 1940's. By 1981 it controlled more than 95% of what has been conceded to be the relevant market. Columbia Outdoor (D) enjoyed close relations with the city's political leaders. In 1981, P began erecting billboards in and around the city. Columbia Outdoor (D) responded, doubling its own billboard construction efforts and modernized its existing stock. It also spread untrue and malicious rumors about P and attempted to induce P's customers to break their contracts. Columbia Outdoor (D) executives met with city officials to seek the enactment of zoning ordinances that would restrict billboard construction. The city council passed an ordinance requiring the council's approval for every billboard constructed in downtown Columbia. This was later amended to impose a 180-day moratorium on the construction of billboards throughout the city, except as specifically authorized by the council. A state court invalidated this ordinance. The city council passed a new ordinance restricting the size, location, and spacing of billboards. These restrictions, particularly those on spacing, benefited Columbia Outdoor (D) and severely hindered P's ability to compete. P filed suit against Ds charging that they had violated §§ 1 and 2 of the Sherman Act. P alleged that the billboard ordinances were the result of an anticompetitive conspiracy between Ds that stripped both parties of any immunity they might otherwise enjoy from the federal antitrust laws. A jury returned general verdicts against Ds. Ds moved for judgment notwithstanding the verdict, contending that their activities were outside the scope of the federal antitrust laws. The District Court granted the motion. A divided panel of the United States Court of Appeals for the Fourth Circuit reversed the judgment of the District Court and reinstated the jury verdict on all counts. The Supreme Court granted certiorari.