Okay kiddo, imagine you're playing with your friend and they suddenly start behaving in a way that's not very nice or friendly. That's kind of like what a hostile witness is in court.
You know how grown-ups sometimes need to go to court to talk about important things that happened? When they do that, there are different people who stand in front of a judge and try to explain what happened.
Sometimes, one of those people doesn't want to help the person who brought them to court. Maybe they don't like that person, or maybe they're scared of getting in trouble if they tell the truth. When that happens, the person talking to the judge might call them a "hostile witness."
That means that even though they're supposed to be helping, the person is making it really hard to understand what happened. They might give short answers, or say things that aren't true. That can be a problem for the judge, because it's harder to make a decision if they don't have all the information.
So, to help fix that, sometimes the lawyer asking the questions will try to ask different kinds of questions or talk to the witness in a different way, in hopes that they'll finally start being helpful.