Counterclaims
Sometimes the defendant has a claim against the plaintiff. In that situation, the defendant can file a counterclaim against the plaintiff in the same lawsuit. By filing the counterclaim, all the disputed issues between the plaintiff and defendant are before the court at the same time.
SIDEBAR: A mandatory counterclaim is a counterclaim the defendant is required to file in the plaintiff's lawsuit because it concerns the same facts and legal issues as the underlying lawsuit. For example, if a tenant is sued by her landlord for damages to an apartment and has a claim for wrongful retention of her security deposit, she must file a counterclaim or waive her right to sue on that issue. In other words, she cannot file a separate lawsuit in the future asking for return of her security deposit.
I filed a lawsuit against my neighbor but did not include her husband in the pleadings. Do I have to file a new lawsuit?
No. You do not file a new lawsuit; you file a new pleading with the husband added. Anytime you want to add or remove from your initial pleading, you are amending the previous pleading.
TIP: Amended pleadings should always be titled "First Amended Petition," "Second Amending Petition" and so on. The amended pleading takes the place of all previous pleadings.