In August, at the start of the school year, Yale’s incoming freshmen were welcomed with daily parties, sunny counsel from deans and advisers, colorful flyers describing clubs and activities, and a more ominous handout: a leaflet decorated with an image of the Grim Reaper. “The incidence of crime and violence in New Haven is shockingly high, and it is getting worse,” the sheet read. A New Haven “survival guide” followed, warning students to “stay off the streets” after dusk, never “walk alone,” and “remain on campus.” The flyer had been designed by the union representing those charged with insuring the students’ safety—the Yale police.New Haven is a compact city of a hundred and thirty-eight thousand people. But its tensions recall those in Philadelphia, Chicago, Los Angeles, or any other ...