More than likely the defendant is using a technicality that can be as simple as the wording in the original filing petition(s). The party involved may be able to modify the suit or may need to refile the entire case. State laws govern the civil action process, therefore any remedy available depends on the applicable state statutes.
In Civil Law, an “answer” is the first formal response given by the defense to a complaint filed with the court by the plaintiff. This opening written statement will admit or deny the allegations, or demand more information about the claims of wrongdoing.
A defense lawyer can sue for malpractice if the subject is breaking the code and conduct of of proper business ettiquette. If the company or individual is in the wrong a malpractice suit can be sought.
In Civil Law, a “complaint” is the very first formal action taken to officially begin a lawsuit. This written document contains the allegations against the defense, the specific laws violated, the facts that led to the dispute, and any demands made by the plaintiff to restore justice.
Your question is too broad to be answered as written, as the nature of the defense depends upon the cause of action asserted by the Plaintiff.
Denial
A counterclaim is an affirmative claim that a defendant in a lawsuit brings against the plaintiff suing him or her. An "affirmative claim" is in addition to the usual defense to a plaintiff's complaint, where the defendant simply denies plaintiff's allegations against defendant. An example is in a car accident case where both sides believe the other was at fault, plaintiff sues defendant for damages from the accident alleging defendant was negligent. Defendant files an answer denying plaintiff's allegations of negligence and adds a counterclaim alleging that plaintiff was negligent and that he or she caused the accident and demanding damages from plainitff. Under rules of procedure, plaintiff usually has to file an answer to the defendant's counterclaim.
release of tortfeasor
Unclean hands, sometimes clean hands doctrine or dirty hands doctrine is an equitable defense in which the defendant argues that the plaintiff is not entitled to obtain an equitable remedy on account of the fact that the plaintiff is acting unethically or has acted in bad faith with respect to the subject of the complaint-that is, with "unclean hands".
The majority of courts generally will not dismiss a complaint at the pleading stag based on affirmative defense, dismissal at this stage may be appropriate when the allegations in the complaint establish the defense.
Statute of limitations
The plaintiff - their legal representative outlines the case for the prosecution. It's then up to the defence barrister to answer the allegations on behalf of the defendant.
It generally means the access by a plaintiff to a lawyer who directs his defense.