Fights broke out in Watford town centre following England's loss to Italy in the Euro 2020 final.
Fans left pubs and bars after the Three Lions' agonising penalty shootout at Wembley.
Tempers were frayed and multiple small fights broke out in the area, and as crowds got larger, the police became a target.
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At around 11.15pm, a police vehicle was kicked by crowds who later fled the scene.
Scuffles also broke out with officers before fans began to disperse.
At least two police vans were seen racing towards Watford from other areas of Hertfordshire to support officers in the town.
Chief Inspector David Partridge, who led the constabulary’s policing response to Euro 2020, said: “As per previous fixtures throughout the tournament, there was a substantial policing operation in place across Hertfordshire for last night’s Euro 2020 final and we worked closely with our partners and licensed premises to ensure everyone enjoyed the game safely.
“It was very busy compared with the previous England fixture and while the majority of fans acted in a responsible manner, sadly there were a few people who let the side down. We had 30 reported incidents throughout the evening, with five arrests."
The constabulary estimates that 400 people were at the town centre after the match.
Many other little fights and violent actions broke out, resulting in a woman taken to hospital after being hit by flying glass, and a man knocked unconscious during an altercation.
He continued: “While we fully understand the disappointment that many people will have felt, there is absolutely no excuse for this kind of behaviour. Follow up enquiries are being conducted at this time and those involved will be dealt with accordingly.”
There was no sign that trouble had occurred in Watford by early afternoon on Monday.
The Parade, where the majority of fans had gathered, was clear of rubbish and there was no visible damage to any buildings or equipment.
It comes after police praised the behaviour of fans who celebrated in Watford on Wednesday after the Denmark semi final victory.
England's wait for a major men's trophy goes on after a 3-2 loss on penalties after the final ended 1-1 after extra time.
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