A mass brawl erupted in Brighton on the eve of lockdown involving a group of about 20 people.
Sussex Police were called to Montpelier Place at 22:15 GMT on Wednesday.
One man suffered serious injuries and was taken to Royal Sussex County Hospital for treatment, where he remains in a serious condition. Four men have been arrested and remain in custody.
The force is appealing for witnesses.
Det Insp Owen Radley said: "The incident happened in what would have been a busy area and we are sure someone would know what happened."