Video of the scene from fan perspective ran wild on social media showing the chaos of the night.
Summer Jam was forced to release a statement on the incident and explained that refunds will be given:
Due to strong demand for tickets for Summer Jam 2015, the show sold out early this evening.When fans realized tickets were not available at the box office, a small number of people created an unsafe environment, and for the safety of all guests, the New Jersey State Police were on scene to disperse the crowd. The gates were closed at that time. No further entry was permitted into the event.For ticket holders whose tickets were not scanned, refunds will be offered at the point of purchase.
H/T Geeks and Cleats