If a jury and a judge decided in favor of the plaintiff in such cases, the plaintiff's claim was not technically frivolous in legal terms, though it might be considered frivolous colloquially. Because of the ambiguity in the term, calling these lawsuits "frivolous" can lead to confusion because opposite sides of the tort reform debate can both say they oppose "frivolous" suits, with the tort reform supporters referring to the colloquial understanding, and tort reform opponents referring to the narrower technical definition.
The typical definition in United States law is very different from its colloquial or political meaning. United States courts usually define "frivolous litigation" as a legal claim or defense presented even though the party and the party's legal counsel had reason to know that the claim or defense had no merit. A claim or defense may be frivolous because it had no underlying justification in fact, or because it was not presented with an argument for a reasonable extension or reinterpretation of the law, or because laws are in place unequivocally prohibiting such a claim (see Good Samaritan law).
In the United States, Rule 11 of the Federal Rules of Civil Procedure and similar state rules require that an attorney perform a due diligence investigation concerning the factual basis for any claim or defense. Jurisdictions differ on whether a claim or defense can be frivolous if the attorney acted in good faith. Because such a defense or claim wastes the court's and the other parties' time, resources and legal fees, sanctions may be imposed by a court upon the party or the lawyer who presents the frivolous defense or claim. The law firm may also be sanctioned, or even held in contempt.
Lawyer Daniel B. Evans writes:
[W]hen a judge calls an argument "ridiculous" or "frivolous," it is absolutely the worst thing the judge could say. It means that the person arguing the position has absolutely no idea of what he is doing, and has completely wasted everyone's time. It doesn't mean that the case wasn't well argued, or that judge simply decided for the other side, it means that there was no other side. The argument was absolutely, positively, incompetent. The judge is not telling you that you were "wrong." The judge is telling you that you are out of your mind.
In the United States Tax Court, frivolous arguments may result in a penalty of up to $25,000 under . Similarly, section 7482 of the Internal Revenue Code provides that the U.S. Supreme Court and the federal courts of appeals may impose penalties where the taxpayer's appeal of a U.S. Tax Court decision was "maintained primarily for delay" or where "the taxpayer's position in the appeal is frivolous or groundless.
In a non-criminal case in a United States district court, a litigant (or a litigant's attorney) who presents any pleading, written motion or other paper to the court is required, under Rule 11 of the Federal Rules of Civil Procedure, to certify that, to the best of the presenter's knowledge and belief, the legal contentions "are warranted by existing law or by a nonfrivolous argument for the extension, modification, or reversal of existing law or the establishment of new law". Monetary civil penalties for violation of this rule may in some cases be imposed on the litigant or the attorney under Rule 11. In one case, the Seventh Circuit issued an order giving such an attorney "14 days to show cause why he should not be fined $10,000 for his frivolous arguments". A similar rule penalizing frivolous litigation applies in U.S. Bankruptcy Court under Rule 9011.
Congress has enacted section 1912 of title 28 of the United States Code providing that in the United States Supreme Court and in the various courts of appeals where litigation by the losing party has caused damage to the prevailing party, the court may impose a requirement that the losing party pay the prevailing party for those damages.
Litigants who represent themselves (in forma pauperis and pro se) often make frivolous arguments due to their limited knowledge of the law and procedure. The particular tendency of prisoners to bring baseless lawsuits led to passage of the Prison Litigation Reform Act of 1995, which limits the ability of prisoners to bring actions.
An example of a Court's treatment of frivolous arguments is found in the case of Crain v. Commissioner, F.2d 1417 (1984), from the United States Court of Appeals for the Fifth Circuit:
Washington, an inmate from Georgia, was eventually prohibited from filing any future lawsuits or motions in any district court unless he first posted a contempt bond of $1,500. To be deemed frivolous, a litigant's arguments must truly strike beyond the pale.
Pearson v. Chung, the case of a Washington, D.C. judge, Roy Pearson, who sued a dry cleaning business for $67 million (later lowered to $54 million), has been cited as an example of frivolous litigation. According to Pearson, the dry cleaners allegedly lost his pants (which he brought in for a $10.50 alteration) and refused his demands for a large refund. Pearson believed that a 'Satisfaction Guaranteed' sign in the window of the shop legally entitled him to a refund for the cost of the pants, estimated at $1,000. The $54 million total also included $2 million in "mental distress" and $15,000 which he estimated to be the cost of renting a car every weekend to go to another dry cleaners.