The holds that contracts or conspiracies in restraint are illegal only if they constitute undue or unreasonable restraints of trade and that only unreasonable attempts to monopolize are covered by the sherman act.

The answer is The Rule of Reason

For Example, a Manufacture company May restrict the supply of a product in different geographic market only to existing Retailers so they can earn a higher profit which lead to them creating a better service to customers.

This policy can increase the demand of the Manufacturer's product