Rule 21 Misjoinder and nonjoinder of parties

Here's a plain English summary:

If a lawsuit includes the wrong people, or too many people, that's not a reason to throw out the whole case. Courts understand that sometimes parties get added to a lawsuit who shouldn't be there, or someone who should be included gets left out. This mistake alone won't kill the case.

Instead, the judge has the power to fix the problem. At any point during the case, the judge can add a person who needs to be part of the lawsuit or remove someone who doesn't belong. The judge can do this on their own, or because one of the parties asked them to. Whatever the judge decides, it has to be fair to everyone involved.

The judge can also split up claims if that makes more sense. For example, if one lawsuit involves several different claims against different people, the judge might decide to separate them into different cases. This helps keep things organized and makes sure each claim gets handled properly, rather than getting the whole case dismissed just because the original grouping of parties wasn't quite right.