A general definition of exclusionary conduct has become a sort of Holy Grail for antitrust scholars. At present, four proposed definitions appear most promising: (1) conduct that could exclude an equally efficient rival; (2) conduct that raises rivals' costs unjustifiably; (3) conduct that, on balance, impairs consumer welfare by creating market power without providing countervailing consumer benefits; and (4) conduct that makes no economic sense but for its exclusionary effect on rivals.
Thomas A. Lambert, Weyerhaeuser and the Search for Antitrust's Holy Grail, Cato Sup. Ct. Rev., 2006-2007, at 277