Why is Max so violent?

It's hard to say for certain, but from the text, we can infer that Max's violent tendencies toward other children, his teachers, and even his grandparents may stem from the fact that his mother is dead, and his estranged father apparently has violent behavior similar to his Max's.

Max is actually a warm hearted boy, but because his dad is known as a serial killer, Killer Kane, kids are afraid of him. His body is bigger than normal kids because his dad also has a strong, huge body. Lot's of people in Max's school judge Max by his apperarence and who his parent was, even though he has the heart of his kind, dead mom, who was murdered by Max's father. He doesn't try to act violent, but sometimes he tends to.