Defining a ‘Market’ Creates Headaches for Antitrust Plaintiffs

Plaintiffs who sue under federal antitrust laws must define a “relevant market” for their allegations, a threshold issue that has become a stumbling block for high-stakes litigation in recent years.

The latest example came Feb. 3, when a federal jury found for US Soccer and MLS in a case claiming they colluded to exclude an upstart league from the top tiers of men’s professional soccer in the US and Canada.

Plaintiffs have to prove that a specific market exists, how that market is controlled by the defendant, and how they were harmed—which the jury said the North American Soccer League ...