It was the quintessential college scene: dozens of students from the Harvard Black Men’s Forum and the Association of Black Harvard Women picnicking on the Radcliffe Quad, playing capture-the-flag and running relay races at their end-of-the-year field day.

But just an hour into the festivities on the sunny afternoon in May 2007, the fun screeched to a halt. Two campus police officers rode up on motorcycles. Were they students? the officers asked. Did they have permission to be there? The young men and women, dressed in Harvard T-shirts, would discover that a fellow student in a nearby dorm had mistaken them for trespassers, according to students who were there and whose account was confirmed by Harvard officials.

The incident, which ignited criticism from black students and faculty, highlighted the prejudices that many black students say they continue to face at Harvard — not only from police, but from classmates as well.