Several police officers were attacked by a group of youths who were trying to cut down a telegraph pole to put on a bonfire.
Police and fire crews were called to Hillbrook Road in Leyland, Lancashire, on Sunday night after reports an unauthorised bonfire was being held.
Youths threw fireworks and bottles at police and seven officers were injured.
Twelve were arrested on public order offences. Three were released without charge and one received an £80 penalty.
Extra patrols were brought in before the situation was brought under control and the fire was put out.
Four of the police officers were treated for their injuries in hospital, but none of them were seriously hurt.