Police are appealing for information after a disturbance outside the Sir Robert Peel pub on Castle Street, Stockport, at around 8.25pm on Friday 17 November.
Officers were called to reports of "windows being smashed" by a group of "youths who approached the pub carrying weapons".
A spokesman for Greater Manchester Police said: "People in the pub went outside and attempted to encourage the group to disperse from the area.
"During this, a man has fallen to the floor and been assaulted by several teenagers."
According to police, the offenders fled from the scene along James Street and onto Booth Street, where one of the youths from the pub was assaulted by members of the public.
He was taken to hospital for treatment for a head injury.
Detective Sergeant Melanie Johnson of GMP’s Stockport borough, said: “This incident escalated quickly and has resulted in two people being assaulted.
“Given that this happened on a Friday evening, near to a busy pub and road, I’d like to speak to anyone who was there at the time, or has information that could help our investigation.
“Additionally I would ask that anyone who has dash-cam footage which might have captured the assault on Booth Street, to contact police.”
- Anyone with information is asked to contact police on 0161 856 9790 or 101, quoting incident number 1988 of 17/11/17. Reports can also be made anonymously through the independent charity Crimestoppers on 0800 555 111.