Explain three reasons why some kids didn't like Maniac.

While Maniac Magee is a relatively easy-going, kind adolescent, his decision to live with the Beales on the East End creates tension in the black community. The town of Two Mills is racially divided into two areas, the East End and the West End. Since Maniac is white, characters like Mars Bar initially bully him and cause him trouble simply because he is a white kid living in the East End. In chapter 17, an old black man during a block party begins calling Maniac Magee a fishbelly and demands that he leave the East End immediately. Similarly, racist white characters like the McNabs and the Cobras dislike Maniac for associating with black people—particularly when he invites Mars Bars over to celebrate Piper's birthday party.
Aside from racial prejudice, characters like John McNab and Mars Bar do not like Maniac because he excels in athletics and embarrasses them in front of their peers. For example, Maniac Magee hits several home runs and even bunts a frogball inside-the-park home run against John McNab, which embarrasses him. On another occasion, Maniac races Mars Bar and beats him running backward.
The third reason people don't like Maniac Magee is simply because he is different. In chapter 16, Spinelli writes that some of the older kids did not like Maniac because he was allergic to pizza, did the dishes without being told to, and never watched Saturday morning cartoons.

In Maniac Magee, racial tensions between residents in different parts of town generate some problems. When Maniac, who is white, goes to live with the Beales, a black family, some other residents of their primarily black East End neighborhood are upset; they reject the boy because of race.
Some of Maniac's specific behaviors, not necessarily attached to race, are bothersome to some people. For example, he gets up early and runs through the streets. Some people object to his running on their street.
In addition, Maniac gains a reputation in the Beales' home for being a cooperative child who does his chores without the adults having to remind him. When other children hear of this, they think that he is strange and that his example might reflect badly on their less cooperative behavior.