It only takes one person. There are a couple of kids at my school who just yell at you for no reason. We talk about issues of violence at my school. We really don't have problems with violence. Kids are killing kids cause people put things in their heads like it would be cool to kill.
Older kids talk younger kids into hitting people up.
They scared that if they don't do it, their friends will disown them. They be trying to do it to be part of something. My friend, last June, he got killed in the neck, he was trying to fit in. It was over a game of craps. He was only 15 and we were real close, since he was six.