A fight erupted between concert goers at New Jersey's Metlife Stadium which required the NJ State Police to make decisions to protect the public. As the fights escalated, the police decided to close the entrance to the concert venue. The crowd's response to the police was to assault the officers with bottles and other objects. The State Police were forced to deploy tear gas to disperse the crowd. Although the police did all they could to protect the people, both officers and concert goers were injured resulting in arrests of over a dozen people.
Yes, the police were justified in their actions against the crowd at Summer Jam 2015. The crowd was unruly and trying to break into a sold out venue that they did not have tickets for. The police are always justified in using force when a group of people turn against them. Throwing trash and other things at police should result in arrests.
From what I understand of the situation, police shut down the concert because a massive crowd of people were trying to rush the gates. Yes, the actions of the police did hurt the people who had paid for their tickets. However, it is the job of the police to keep everyone safe and in order, and that is exactly what they did. Refunds were issued to the people who paid and did not get in.
There was no need for police to go to the extent in which they did at summer Jam 2015. There actions could have caused more harm than good for the public, and their job is to protect, not to further harm. There could have been other actions taken to calm and contain the crowd than what the police decided to do.