Incompetent evidence refers to documents, testimony, or any other thing which is presented by one party as a proof against another during a lawsuit, and which the court finds immaterial or irrelevant with respect to issues being discussed in that trial.
It is usually after the objection is raised from the opposing party that the court declares an evidence incompetent and declares it “not admissible.” Evidence may be deemed incompetent due to lack of originality, nature of evidence, defect in witness, etc.