In 1964, Bangor Punta Operations, Inc. (Bangor Punta) (defendant) acquired 98.3 percent of the stock of Bangor & Aroostook Railroad (BAR) (plaintiff). In 1969, Bangor Punta sold its interest in BAR to Amoskeag Co. (Amoskeag). Amoskeag later purchased additional stock in BAR, giving Amoskeag between 99 and 100 percent of BAR stock. In 1971, BAR—at that point controlled by Amoskeag—brought a shareholder suit against Bangor Punta in the United States District Court for the District of Maine under § 10 of the Clayton Act and § 10(b) of the Securities and Exchange Commission Act of 1934, alleging severe mismanagement of BAR between 1960 and 1967. The district court granted Bangor Punta’s motion for summary judgment, finding that because the alleged harm occurred prior to Amoskeag’s purchase of the BAR stock, any recovery for Amoskeag under the BAR moniker would be a windfall. BAR appealed, and the United States Court of Appeals for the First Circuit reversed. The United States Supreme Court granted certiorari.