Arsenal and Cologne are facing disciplinary proceedings by European football's governing body UEFA after 20,000 fans of the German club descended on London, reports CNN.
Labelled as "sporadic disorder" by British police and "jovial" by others, Arsenal's Europa League match against Cologne on Thursday divided opinion of those in the stands and watching on television.
Despite only being given 3,000 official tickets, thousands of other Cologne fans flocked to London in celebration of the club's first appearance in European competition for a quarter of a century.
Earlier on Thursday it became clear this was going to be no ordinary European football game as thousands of chanting Cologne fans marched through central London.
Later some quick-witted Cologne fans even bought themselves Arsenal scarves and changed the backgrounds on their phones to the Gunners' club crest to gain entry using home tickets.
"There were also a number of incidents resulting from sporadic disorder inside the ground after away fans gained access to seating assigned to Arsenal supporters," said the Metropolitan Police in a statement.
"As a result of these actions, kickoff was delayed for almost an hour.
"Additional officers and police dog units were deployed to the area to respond to the disorder. Three officers were injured as a result of the disorder, none of them seriously, and five people were arrested on suspicion of public order offences."
According to latest statistics, nearly 2,000 football-related arrests were made in the 2015-16 season at matches in England and Wales, a 1 % increase on the previous and the first rise for three years.
However, home and away fans also mixed peacefully in the stands and on the concourse, exchanging renditions of their favourite club songs at Thursday's match.
"Loudest away support I've ever seen at a game in England," said leading footballer writer Michael Cox on his Instagram account.
In opening disciplinary proceedings, European football's governing body's investigation will look at disturbances, setting off fireworks, throwing of objects, acts of damage and blocked stairways.
"This will be dealt with by the UEFA Control, Ethics and Disciplinary Body on September 21," a UEFA statement read.
