Adverse Interest

The legal right or liability of a person called to testify as a witness in a lawsuit that might be lost or impaired if the party who called him or her to testify wins the case.

This interest against the interest of the party calling a witness to the stand makes him or her an adverse or hostile witness. Although usually the party calling a witness to testify cannot impeach that person's credibility, if the person has an adverse interest, the testimony may be discredited by the party who called that witness to the stand.