A defendant's claim is the form filed by a defendant who wishes to sue the plaintiff for money damages. A defendant's claim should be filed with the clerk and served on the plaintiff within the proper number of days before the hearing. Days are counted in the same way as discussed above.
If you are a defendant who has filed a claim and you are unable to serve the plaintiff, simply show up on the court hearing date with your papers and serve the plaintiff in the hallway (not in the courtroom). Then explain to the judge why it was impossible to locate the plaintiff earlier. The judge will normally delay the case for a few days, unless both you and the plaintiff agree to proceed with your claim that day. Either way, the judge should accept your defendant's claim as having been validly served.