Why does Uncle Jack punish Scout in To Kill a Mockingbird?

When Scout's cousin Francis called Atticus all sorts of names because he's defending a black man, Scout gets into a fist fight with him. At that moment Uncle sees her and chastises her for fighting, not giving her a chance to tell her side. Later in the evening she is finally able to explain the situation to him and he apologizes to her.

scout got upset with uncle jack cause he wouldn't listen to her side of the story.