In the United States v. Munsingwear, Inc., 1950 case, the U.S. Supreme Court addressed a situation where an appeal was moot due to circumstances outside of the appellant's control and without any fault on their part. The government had filed an antitrust suit against Munsingwear for selling products at fixed prices. While this case was pending in district court, another circuit court ruled that such price-fixing arrangements were legal under certain conditions which applied to Munsingwear’s case as well. Consequently, the district court dismissed the government's complaint as moot based on this ruling from another jurisdiction before it could be appealed by them. The Supreme Court held that when a civil case becomes moot while pending on appeal due to happenstance (i.e., external factors beyond either party's control), lower courts should dispose of it "in a manner consistent with equity" rather than simply dismissing it outright or leaving its resolution unaddressed - essentially vacating or setting aside any judgment below and remanding with directions to dismiss. This decision established what is now known as 'the Munsingwear doctrine', providing guidance for how federal courts should handle cases rendered moot during pendency of appeals.

In the dissenting opinion for United States v. Munsingwear, Inc., Justice Douglas argued that the majority's decision to vacate and remand the case was unnecessary and inappropriate. He contended that there were no exceptional circumstances warranting such action, as required by established precedent. Furthermore, he disagreed with the majority's interpretation of Rule 60(b) of Federal Rules of Civil Procedure which allows a party to seek relief from a final judgment under certain conditions. In his view, this rule did not apply because it was intended for situations where judgments are obtained through fraud or mistake - neither of which occurred in this case. Instead, he believed that since both parties had ample opportunity to present their arguments before lower courts and failed to do so effectively resulting in dismissal due to mootness; they should bear consequences rather than having another chance at litigation.