What are three reasons in Chapter 1-9 that show why Maniac Magee is a maniac?

Jeffrey Magee is known as “Maniac Magee” because he engages in behaviors that everyone considers impossible. 

Jeffrey gets the nickname Maniac by herding the frog McNab is using as a baseball. 

… McNab was lurching and lunging, throwing his hat at the frog, throwing his glove, and everybody was screaming, and the kid was rounding third and digging for home, and --unbefroggable! -- the "ball" was heading back home too! … (Ch. 7) 

It was “the world's first frogball for a four-bagger.” Bizarre incidents like this one gave Maniac his nickname.  He seems to be able to do things that others can’t or won’t do. 

Another example of Maniac’s growing legend is the incident at Finsterwald’s.  The Finsterwald house is considered dangerous, and no neighborhood kids will go near it.  Maniac, not knowing this, rescues a kid that some older kids are hassling by getting him off Finsterwald’s land.  Then Maniac sits on the porch and reads a book.  This was one of the first crazy things Maniac did, and his legend only grew from there. 

He was running, passing the spear field now, and the Pickwell kids had to blink and squint and shade their eyes to make sure they were seeing right -- because the kid wasn't running the cinders alongside the tracks, or the wooden ties. No, he was running - running -- where the Pickwells themselves, where every other kid, had only ever walked --on the steel rail itself! (Ch. 6) 

Maniac also stared down Mars Bar, raced him backward, and tried to unite the East and West Sides.  These two sides were divided by race.  Maniac is attacked by the Cobras, a race-oriented gang who track him down.  They are shocked to see a boy with a book running on the rail.  Eventually, Maniac even befriends them.  There seems to be no one who doesn’t like him.