EAST RUTHERFORD, N.J. — It seems that every year of late, the annual Summer Jam presented by the radio station Hot 97 has to find new purpose. In the 1990s and into the mid-2000s, it was the New York hip-hop concert of record. Now it is a showcase for the genre’s scattered regional identities and Hot 97’s decreasingly steady footing as an arbiter of its future. Summer Jam was once the essential proving ground; now it’s a hit-or-miss revue.

This year, the headliner was Kendrick Lamar, a B-list version of an A-list star. He’s popular but not especially accessible, the most cerebral hip-hop star of the day and also one of the most tepid. (And also from Los Angeles, as it happens.) As he was performing a committed but cool set full of knotty verses on the MetLife Stadium stage here Sunday night, the crowd regarded him with something less than ebullience. In the absence of Drake, Kanye West or Jay Z, this would have to do.

But outside, Summer Jam was facing a more troubling crisis. There was a face-off between would-be concertgoers (some with tickets, some apparently without) and the police. The entrance gates had been shut. Videos and photos posted on social media showed a brawl at a ticket window, people climbing a tall fence to get into the arena, others throwing objects at the police, the police carrying riot shields. Hundreds, if not thousands, of ticket-holding fans were turned away and sent home.