hostile witness
noun /ˌhɒstaɪl ˈwɪtnəs/
/ˌhɑːstl ˈwɪtnəs/, /ˌhɑːstaɪl ˈwɪtnəs/
(law)- a person who must answer questions in court but might not want to tell the truth or might answer in a way that is bad for the people asking the questions
- She was declared a hostile witness, then cross-examined.