During an examination-in-chief , a lawyer is not allowed to ask leading questions of their own witness. But, if that witness openly shows hostility against the interests (or the person) that the lawyer represents, the lawyer may ask the court to declare the witness "hostile", after which, as an exception of the examination-in-chief rules, the lawyer may ask their own witness leading questions.
HOSTILE WITNESS
Meaning of HOSTILE WITNESS in English
Duhaime's Law English dictionary. Английский юридический словарь Duhaime . 2012