How does Maniac keep John McNab from fighting with Mars Bar?

When a fight nearly broke out between John McNab and Mars Bar, Maniac stepped in and simply led Mars Bar away from the McNab home.

Explanation:

Maniac was instrumental in bringing Mars Bar to the McNab's home for the birthday party. But Mars Bar was uncomfortable being in a white home and the McNab family were uncomfortable having a black in their home. When the McNab boys played the game "blacks and whites", it made Mars Bar very uncomfortable.

Maniac's purpose of inviting Mars Bar to the birthday party was to teach Mars Bar about the white people and to teach the white about the blacks. But it wasn't actualized.

"Maniac Magee" is a story by American author Jerry Spinelli. The story's themes center on racism and inequality. It tells the story of an orphan boy who was looking for an abode and a home in the fictional town of Two Mills. Two Mills is a town which was torn between the East and West, blacks and whites.