The party opposite the defendant goes by different names depending on the type of case. In a civil lawsuit, that party is the plaintiff. In a criminal prosecution, it’s the prosecutor, acting on behalf of the government. Other proceedings use their own labels: petitioner in family court and many administrative hearings, claimant in arbitration, and appellant once a case reaches an appeals court. Each label tells you who started the proceeding and what kind of proceeding it is.
Plaintiff: The Opposite of Defendant in a Civil Lawsuit
A plaintiff is the person or entity that files a civil lawsuit against the defendant. Slip on a broken staircase and sue the property owner for your medical bills, and you’re the plaintiff. The owner is the defendant. The plaintiff starts the case by filing a complaint that lays out the alleged wrongdoing and the remedy sought, whether that’s money, a court order to stop certain behavior, or something else.
The plaintiff carries the burden of proof. In most civil disputes, that means proving the claim by a “preponderance of the evidence” — more likely than not. If the plaintiff’s version of events is even slightly more convincing than the defendant’s, the plaintiff wins on that point.1Legal Information Institute. Burden of Proof That’s a much lower bar than what prosecutors face in criminal court.
Prosecutor: The Opposite of Defendant in a Criminal Case
Criminal cases work differently because the victim doesn’t personally sue the accused. A prosecutor represents the government instead. You can see this in case names like “State v. Smith” or “United States v. Jones.” The prosecutor is the official party opposite the defendant, acting on behalf of the public rather than any individual.
Because a conviction can mean prison time, the prosecutor faces a tougher standard than a civil plaintiff. The prosecution must prove guilt “beyond a reasonable doubt,” the highest standard in the legal system.1Legal Information Institute. Burden of Proof That doesn’t mean every conceivable doubt, but the evidence has to be strong enough that a reasonable person wouldn’t seriously question whether the defendant did it.
One term that sometimes causes confusion is “complainant.” In criminal matters, the complainant is the person who reports the crime or the alleged victim. The complainant is not a formal party to the case the way a plaintiff is in a civil lawsuit. The prosecutor alone decides whether to bring or drop charges, regardless of what the complainant wants.
Petitioner in Family Court and Administrative Hearings
Not every proceeding fits the plaintiff-defendant or prosecutor-defendant mold. In family court, probate, immigration hearings, and many administrative proceedings, the initiating party is called the petitioner and the other side is the respondent. A person filing for divorce, requesting a restraining order, or seeking guardianship of a minor files a petition rather than a complaint. The other party responds to it.
The practical difference from a standard civil lawsuit is often just procedural. Petitions tend to ask the court for a specific order or ruling rather than money damages, though that isn’t a hard rule. In some courts, these terms are used interchangeably with plaintiff and defendant. What matters is the underlying dynamic: one party started the action, and the other is answering it.
Claimant in Arbitration
When disputes go to arbitration instead of court, the terminology shifts again. The party who initiates the arbitration is the claimant (sometimes called the petitioner), and the other side is the respondent. Organizations like the American Arbitration Association and FINRA run these proceedings under their own procedural rules, which differ from what you’d see in a courtroom. Despite the different labels, the claimant-respondent relationship mirrors the plaintiff-defendant one: one side brings the claim, the other answers.
Appellant on Appeal
When a case moves to an appeals court, the party labels change entirely. The person who files the appeal is the appellant (or petitioner), and the person defending the lower court’s decision is the appellee (or respondent).2Legal Information Institute. Appeal Either side from the trial can end up in either role. If a defendant loses at trial and appeals, the defendant becomes the appellant and the original plaintiff becomes the appellee. If the plaintiff is the unhappy one, the roles flip.
Things get more interesting when both sides are unhappy. Say a jury awards the plaintiff damages but less than the plaintiff wanted, and the defendant thinks the verdict was wrong altogether. Whoever files first is the appellant. The other party’s filing is called a cross-appeal. The labels are determined by who files first, not by who was plaintiff or defendant at trial.3Legal Information Institute. Cross-appeal A cross-appeal only exists when the second party is actively asking the higher court to change the lower court’s ruling. Simply asking the court to leave the ruling alone doesn’t count.
When the Defendant Fights Back
A defendant doesn’t have to stay on defense. If the defendant has their own claim against the plaintiff, they can file a counterclaim within the same lawsuit. At that point, the defendant is essentially acting as a plaintiff on the counterclaim, and the original plaintiff has to defend against it. The whole thing gets resolved in one case rather than two.
Federal rules divide counterclaims into two categories. A compulsory counterclaim arises out of the same events as the plaintiff’s original claim. If the defendant doesn’t raise it during the lawsuit, it’s gone for good. A permissive counterclaim involves an unrelated dispute between the same parties, and the defendant can choose whether to include it or save it for a separate lawsuit later.4Legal Information Institute. Rule 13 – Counterclaim and Crossclaim That “use it or lose it” rule for compulsory counterclaims is where people get tripped up. If your counterclaim is logically related to the plaintiff’s suit and you stay silent, you’ve waived it.
Defendants can also bring new parties into the lawsuit. Under federal rules, a defendant who believes a third party is responsible for all or part of the plaintiff’s claim can file a third-party complaint. The defendant becomes a “third-party plaintiff” for that claim, and the new party becomes the “third-party defendant.”5Legal Information Institute. Rule 14 – Third-Party Practice If the defendant files that third-party complaint more than 14 days after serving the original answer, the court’s permission is required first. Cross-claims work similarly but involve parties already on the same side of the case, like one co-defendant suing another over who’s actually at fault.
Quick Reference for Party Names
- Civil lawsuit: Plaintiff (files the case) vs. Defendant (responds to the case)
- Criminal case: Prosecutor (brings charges on behalf of the government) vs. Defendant (the accused)
- Family court and administrative proceedings: Petitioner (files the petition) vs. Respondent (answers the petition)
- Arbitration: Claimant (initiates the arbitration) vs. Respondent (answers the claim)
- Appeals: Appellant (files the appeal) vs. Appellee (defends the lower court’s decision)
- Counterclaim within a lawsuit: The original defendant becomes a counter-plaintiff; the original plaintiff defends against it