Hector Street is the racial divide in the town, where the neighborhood on one side is inhabited by white people and the neighborhood on the other side is inhabited by black people. Maniac Magee is the only child who crosses these invisible barriers-- he is not deterred by race. However, the McNabs have been brought up in a racist environment and see the blacks as enemies, even playing games in which they build forts and battle the black people. Therefor, when they reach Hector Street, they do not cross it, despite all their bravado. Hector Street is important in the novel as this invisible racial divide, even Amanda Beale knows she's not supposed to go over to the white side. However Maniac crosses those lines, and eventually brings the two sides together. His actions teach the lesson that people, regardless of race, are more alike than people think. At the core of every human there is love and good.
McNab's group stoped at Hector Street because that is where the town is divided. On the west side is the white neighborhood and on the east side is the black neighborhood. Maniac doesn't mind to cross Hector to either side, because he doesn't see anything with the racism that goes on. McNab's group is racist and they laugh at Maniac when he crosses, because he is on the "wrong side" now. The group thinks Maniac will get beat up for being a different race.
In Maniac Magee the Mcnabs stopped at Hector street because that where the east end and the west end are seperated