A person or entity who is not a party to a lawsuit generally may intervene in the lawsuit and become a party to it by filing a plea in intervention prior to the entry of the court’s judgment—provided the court does not reject (strike) the intervention. An intervenor is not required to secure the court’s permission to intervene, and the party who opposed the intervention has the burden to challenge it by filing a motion to strike.

A person or entity has a right to intervene if the intervenor could have brought the same lawsuit, or any part of it in his own name—or, if the action had been brought against him, he would be able to defeat the lawsuit, or some part of it.

A trial court abuses its discretion by striking an intervention if (1) the intervenor meets the above test, (2) the intervention will not complicate the case by an excessive multiplication of the issues, and (3) the intervention is almost essential to effectively protect the intervenor’s interest.

In West Virginia, the rules regarding intervention in a lawsuit are similar to those described. A person or entity not originally part of a lawsuit may intervene by filing a plea in intervention, typically before the court has entered a judgment. The right to intervene is granted if the potential intervenor has an interest that could have led them to initiate the same lawsuit or defend against it. The court does not need to grant permission for the intervention, but the party opposing the intervention can challenge it by filing a motion to strike. The burden of proof lies with the party opposing the intervention. A trial court may be found to have abused its discretion if it strikes an intervention when the intervenor meets the criteria of having a stake in the outcome, the intervention does not unduly complicate the case, and the intervention is necessary to protect the intervenor’s interests. It's important to note that while these principles provide a general framework, specific cases may be subject to additional rules or interpretations by the courts, and an attorney can provide guidance on the particular circumstances of a case.