When do people use judo?

When someone tries to rob you, you're allowed to use the judo. When someone tries to assault you, you tell them to stop. If they try again, you warn them about what you're gonna do if they don't stop. If they try a third time, you use the judo. If you don't know how the art of self defense works, you can watch videos and you can take martial art lessons like judo or karate. But you're only allowed to use it when someone tries to attack you.