what is the order protection rule 
the order protection rule is one of the four main provisions of the regulation national market system nms the rule is meant to ensure that investors receive an execution price that is equivalent to what is being quoted on any other exchange where the security is traded the rule eliminates the possibility of orders being traded through which means executed at a suboptimal price 1 the order protection rule requires that each exchange establishes and enforces policies to ensure consistent price quotation for all nms stocks which include those on the major stock exchanges as well as many over the counter otc stocks the order protection rule rule is also known as rule 611 or the trade through rule 2 