The bands pulled their van in the back alley to load out as the usual process, the South Street bike cops came through the alley, yelling at the bands to move their vans because they were not allowed to park. The bands asked the cops if they could have a few extra minutes so they could get all their gear out.
Four tickets were written and it upset Trevor (tour manager) so he tried to contest them and was arrested for what I'm assuming to be "obstruction of justice." As they had him in handcuffs, Chris (who sells merch on the tour) tried to come outside to contest his arrest, he was yelled at to stay inside and in discussion the police lost patience and literally beat him back inside the door, then to the ground, and arrested him for "assaulting a police office" when he did not touch them nor gave them any incentive to think they were in danger.
An office has the right to use force when he fears his own safety is in danger. A verbal argument is not justification to beat an innocent bystander with metal batons. After the cuffed him and picked him up, a large pool of blood was on the ground where his head was.
Some video of the incident was shot. An account of the incident was also reported by the Philadelphia Inquirer.