The young men who call themselves Gangster Disciples skirted by an empty lot. They marched past a “Stop the Violence” mural painted on a corner store, coming to a halt when they saw members of a rival gang, the Black Disciples. It was late September on a busy South Side intersection, and now tensions were escalating, gang members who were there recalled. There were glares, they said. Then words. “You’re a rat,” a Black Disciple said to one of the Gangster Disciples who he believed had given the police information about him.