Whether courts must analyze both sides of a two-sided platform with indirect network effects in defining the relevant antitrust market, as required by Ohio v. American Express Co.

QUESTIONS PRESENTED This antitrust case presents two important federal questions concerning whether courts will apply—or contravene—this Court’s landmark decisions in Ohio v. American Express Co., 585 U.S. __, 188 S. Ct. 2274 (2018) (“Amex”), and Illinois Brick Co. v. Illinois, 431 U.S. 720 (1977) (Illinois Brick”). Here, the Ninth Circuit failed to follow either decision, sowing confusion and inviting future courts to ignore or misapply fundamental principles of antitrust law. The Ninth Circuit’s ruling presents the following two pressing questions for this Court’s consideration. First, in defining the relevant antitrust market for a two-sided platform with indirect network effects, can courts simply elect not to analyze both sides of the market, notwithstanding this Court’s command that they “must” do so? See Amex, 138 S. Ct. at 2286. Second, where Illinois Brick established the “indirect purchaser” rule such that the first party outside the conspiracy has standing to sue, can a competitor establish standing based on harm to alleged members of the conspiracy? This case concerns Petitioners’ well-established multiple listing services (“MLS”) platforms that facilitate home real estate sales nationwide—a industry responsible for 17 percent of the nation’s Gross Domestic Product. For this substantial market—and manifold other two-sided platforms— this Court’s review will provide much-needed guidance to ensure that courts follow Amex and Illinois Brick, and not the Ninth Circuit’s contrary and erroneous approach. (i)