There are always at least two sides to the story, and very often when a plaintiff files a lawsuit, the person or business being sued also has a dispute or potential claim against the plaintiff. If your claim is related to the one in the lawsuit (for example, if you are being sued for breaching a contract you may also believe the plaintiff breached the same contract), then you must bring it is a counterclaim in the same action.
This means that when your attorney files an answer to the plaintiff's complaint he or she will also lay out your counterclaim in the same document, which the plaintiff will have to answer in the time allowed under the rules. If your complaint is not related to the events raised in the original complaint, you may still want to assert the counterclaim in the same action, either for a strategic purpose or simply to put all of the issues on the table in the same proceeding. Our initial assessment of your defenses to the claim always includes an assessment of claims you may have against the plaintiff so that you can make an informed decision about whether to include them in the lawsuit.