Antitrust litigation often requires courts to consider challenges to vertical “control.†How does a firm injure competition by limiting the behavior of vertically related firms? Competitive injury includes harm to consumers, labor, or other suppliers from reduced output and higher margins.Historically antitrust considers this issue by attempting to identify a market that is vertically related to the defendant, and then consider what portion of it is “foreclosed†by the vertical practice. There are better mechanisms for identifying competitive harm, including a more individualized look at how the practice injures the best placed firms or bears directly on a firm’s ability to reduce output and increase its price without losing so many sales that the price increase is unprofitable.