Disorder caused by fans around Brighton's match against Crystal Palace on Tuesday has been described as a "return to the dark days of football'' by Sussex Police.
Chief Inspector Simon Nelson, who led the policing operation for the fixture, described how "groups of masked people'' sought confrontation and supporters tried to gain entry to the Amex Stadium with "pyrotechnics, knives and knuckledusters.''
Nelson also revealed that at one stage a large number of people, seemingly without tickets, over-ran turnstiles in the ground's south stand to force access to the away supporters' section.
Disturbances also broke out at Brighton railway station, where frustration grew among fans set to miss the start of the match.
Six people, including one 15-year-old boy, were arrested, while two stewards -- one from each club -- had to be taken to hospital, one with three fractured ribs.
Both stewards were discharged later on Tuesday night.
Nelson said: "I have been involved in football policing at all levels and have been a match commander for Albion matches for 12 years, but I have never come across such concerted attempts to cause disorder and engage in violent behaviour.''
Nelson added: "This was a return to the dark days of football and is not acceptable.''
Palace have said there are clear images of the disturbance and that fans involved will face stadium bans and possible criminal action.
A Crystal Palace statement read: "We have been made aware of a small group of supporters attempting to gain access to the Amex stadium last night without tickets while using bangers and flares.
"This kind of antisocial and criminal behaviour is completely unacceptable and we condemn it in the strongest possible terms.
"There are very clear images of the incident and we will work with the police to identify the supporters involved, who will face stadium bans as well as potential criminal proceedings.
"We would like to apologise to all the innocent supporters who arrived at the stadium with tickets but were denied entry and to the two stewards who were injured at the ground. We wish them a full and speedy recovery.''
Brighton chose to close the stadium's turnstiles at 7:51 p.m., six minutes into the match, which finished goalless.
That decision left some fans with legitimate tickets locked outside the ground, and they were escorted back to the railway station and sent back to London.
Palace said any supporters with unscanned tickets, who were denied entry to the match, could contact the club for a refund.
Brighton chief executive Paul Barber said: "Firstly, we hope the two stewards hospitalised in the disorder have not suffered serious injuries.
"The disorder was caused by a minority of individuals who attempted to gain entry to the stadium without tickets.
"Thanks to the swift action of the club's stewarding team, supported by Sussex Police, we avoided further, major disorder -- and while some genuine fans were left extremely disappointed and unable to get into the stadium, the correct decisions were made.
"I'd like to thank the majority of fans of both clubs for their good behaviour and patience in complying with the instructions of our stewards and police.''
Two men have been charged with using threatening, abusive, or insulting words or behaviour and another with being a football spectator failing to comply with a banning order.
One man and one 15-year-old boy were arrested on suspicion of throwing or discharging a missile and have been released under investigation.
Another man was arrested on suspicion of using threatening, abusive or insulting words or behaviour to cause harassment, alarm or distress. He remained in custody on Wednesday.
Press Association Sport reports the Football Association regard the matter as primarily one for Sussex Police and will support any investigation made.
The FA will also seek observations from Brighton as the host club.