This Article considers how antitrust’s rule of reason should be applied to an exclusionary practice on a platform market. It considers the rule of reason’s basic burden-shifting framework, unique elements of market delineation on platform markets and the relevance of placing production complements into the same “market.” It also considers the Court’s regressive, antieconomic conclusion on a proposition that was never briefed—whether a market definition is necessary in an antitrust challenge to a vertical practice. Then it considers the Court’s odd treatment of free rider problems. It also faults the Court for paying so little attention to the record, its lack of economic analysis, and in particular its confusion of total with marginal harms and benefits. Finally, it looks at the implications of the Court’s decision for market delineation in cases involving platforms.