Final answer:
The antitrust principle most often used by physicians to challenge decisions about medical staff privileges is the principle of restrictive practices.
Step-by-step explanation:
The antitrust principle most often used by physicians to challenge decisions about medical staff privileges is the principle of restrictive practices. Antitrust law includes rules against practices that might have the effect of reducing competition, even if they don't involve outright agreements to raise prices or reduce quantity produced. In the case of physicians challenging decisions about medical staff privileges, they may argue that certain policies or agreements restrict competition and limit their ability to practice medicine.