A more thorough explanation:

A hostile witness is someone who is called to testify in a court case but ends up giving answers that are not helpful to the side that called them. This can happen when the witness has a bias against the side that called them or when they are afraid to tell the truth. The examiner may ask leading questions to try to get the witness to say what they need to hear.

In a criminal trial, the prosecution calls a witness who saw the defendant at the scene of the crime. However, when the witness takes the stand, they refuse to answer questions or give vague and unhelpful answers. The prosecution may declare the witness to be hostile and ask leading questions to try to get them to say what they saw.

Another example could be a witness who has a personal grudge against the party that called them. They may intentionally give false or misleading testimony to hurt that party's case.

These examples illustrate how a hostile witness can be a challenge for the side that called them, as they may not get the information they need to prove their case.