Police swooped on a Blackpool fast food restaurant last night after reports of fight outside.
An officer and a man in his 40s were assaulted during the melee, police said.
Witnesses described scenes of “madness” after several police vehicles pulled up outside KFC, on Lytham Road, at around 9.30pm on Sunday.
Pictures from the scene appear to show police handcuffing a youth, who was seen pinned to the floor.
One eye-witness said the youths targeted a customer who was inside KFC.
Sue Bland, who lives nearby, said: “There were about 50 of them outside – they were banging on the window.
“It was absolutely disgusting what the youths were doing.
“Those police officers deserve a medal for what they had to put up with last night. They were trying to calm them down.”
Although some people have taken to social media to criticise the police for being too heavy-handed, she said the arrests were a “last resort”.
“The kids were shouting and spitting at them,” she added. “They needed throwing to the floor.
“I have never seen anything like it in my life.”
A Lancashire Police spokesman said: “We got a report at 9.25pm that a group of teenagers were fighting outside KFC.
“An officer has been assaulted and a man in his 40s was verbally abused by a group of youths. He has been pushed but not injured.”
Three people, all from Blackpool, were arrested following the disturbance.
A 37-year-old man was arrested on suspicion of assaulting a police officer, a 17-year-old girl was arrested for a public order offence and an 18-year-old man was arrested on suspicion of assault.
All three were still in custody on Monday.