Police are confident they will soon identify dozens of football fans involved in mass violence that resulted in a man having his face slashed.
Rival groups clashed in ugly scenes before and after the Millwall v Everton FA Cup game on Saturday in London, some of which appeared to be organised encounters, Scotland Yard said.
Millwall's dramatic 3-2 win at the Den was further marred by videos appearing to show some home fans singing racist chants.
Both police and the Football Association are investigating the alleged incident.
Specially trained police had to be deployed to help the 200 officers on duty for the match as the violence escalated, with videos online showing dozens of men trading frenzied punches.
One man, who identified himself on social media as Everton fan Jay Burns, suffered a "horrific, life-changing injury" as he was slashed the length of his face, deputy assistant commissioner Matt Twist said.
Mr Twist praised officers for their "determination in restoring order" despite "furniture, bottles and glass being thrown at them" and said one officer injured trying to control the crowds has been released from hospital.
Speaking outside New Scotland Yard on Monday, Mr Twist said the clashes were "some of the most shocking football violence we have seen for some time" and "it would seem likely as though there were an arranged meet".
He said: "Dedicated evidence-gatherers put themselves in harm's way in significant danger and obtained significant and substantial amounts of evidence and footage of the disorder.
"I am confident we will soon know the identities of those involved.
"We will use this evidence and all of the tools within our power to locate the individuals involved in this ridiculous behaviour whether they come from London, Liverpool or elsewhere. We will bring them to justice."
Mr Twist estimated up to 50 people were involved in the worst elements of the violence, which he described as "the worst that we've seen for some time, certainly in London".
A number of coaches carrying Everton fans were also damaged during the disorder, which went on for "some considerable period of time", he said.
He added: "The mobility, the geography, a number of factors led to the violence escalating.
"How it got to that level will form part of the inquiry."