Columbia Outdoor Advertising, Inc. (COA) (defendant), maintained a billboard business in the City of Columbia, South Carolina (the city) (defendant). COA had been a staple of the Columbia community for many years, and COA had strong relationships with local political leaders, including members of the city council. In 1981, Omni Outdoor Advertising, Inc. (Omni) (plaintiff), decided to enter the South Carolina market and began putting up billboards in Columbia. By then, COA enjoyed a 95 percent share of the market. Competition between Omni and COA escalated, and eventually COA met with city officials to establish new billboard regulations. In 1982, the city enacted an ordinance that restricted the location, dimensions, and apportionment of billboards within the city. Because COA already had billboards in place, the ordinance had a significant effect on Omni’s, but not COA’s, ability to compete. Omni responded by bringing an action against the defendants, alleging antitrust violations under the Sherman Act. Omni argued that the defendants had conspired with anticompetitive intent and were not entitled to antitrust immunity under the state-action doctrine. A jury returned a verdict for Omni and awarded damages, but the district court granted the city’s motion to overturn the verdict. The court of appeals reversed the district court’s judgment and reinstated the jury verdict. The defendants appealed.