A man has suffered a slash wound to the face after "disgraceful" disorder ahead of an FA Cup match, police said.
Crowds clashed in Southwark, south London, before Millwall took on Everton in the FA Cup fourth round.
The Metropolitan Police said on Twitter that they believed the fight was between Millwall and Everton fans.
Video posted on social media shows police attempt to separate two large groups as punches were thrown.
Officers were called to the scene on Hawkstone Road, Southwark, shortly after 4.30pm, and are urging anybody with any information to come forward.
Police are investigating after a large group of males, believed to be Millwall and Everton fans, began fighting in the street in #Southwark earlier today. Those with info that could assist police should call 101 ref 5117/26 Jan https://t.co/Xl9a3HzTZM pic.twitter.com/RmEY0JaIze— Metropolitan Police (@metpoliceuk) January 26, 2019
Detective Inspector Darren Young said: "The behaviour of those involved in this incident is nothing short of disgraceful and those involved can be certain we will be working to identify them.
"We are aware of the video circulating online which has quite rightly elicited shock and disgust.
"We are looking at it and urge anyone with information that could assist police to call 101."