Antitrust law has long been concerned that the loss of a firm, through merger or exclusion, may improve the prospects for tacit or express collusion in a concentrated market. In merger law, this perspective has been codified as a presumption of anticompetitive effect arising from high and increasing market concentration. Antitrust's structural presumption has been eroding in the courts, however, in part because its economic underpinnings increasingly are seen as unsettled. This Article explains how coordinated competitive effects analysis can be reconstructed around the role of a maverick firm that constrains prices when industry coordination is incomplete. Doing so helps distinguish procompetitive mergers from anticompetitive ones, and may aid in the analysis of alleged exclusion. It also provides a new economic justification for the structural presumption and points toward a continuing role for that presumption when the maverick cannot be identified or when it is not possible to determine the effect of a merger on the maverick's incentives. The resulting approach to coordinated competitive effects analysis is illustrated with an extended example involving oligopoly conduct in the U.S. passenger airline industry.