Gangs of hardcore football fans went out to hunt down and attack Liverpool supporters in Naples ahead of their goalless draw, Italian police said.
There were several incidents on Wednesday night, ahead of Liverpool's Europa League tie at Napoli's Stadio San Paolo on Thursday.
Three Liverpool fans have been treated in hospital for stab wounds. Four others were also injured.
Italian police stepped up security ahead of the game.
One of the men who was stabbed has since been released from hospital.
Two others, 53-year-old Alexander Phillips, of Liverpool, and a 27-year-old who is not being named, are due to be released from hospital later, the BBC's correspondent in Rome, Duncan Kennedy said.
Mr Phillips had injuries to his buttocks and thighs, and the other man was wounded in the head, he said.
The other four were injured when they were attacked by a group of 20 to 30 men.
Gary Brown, 50, from Hertfordshire, and his son Adam, 17, received a knife injury and bruising respectively.
Mr Brown's other son Daniel, 23, was not injured but family friend Ross Hazeldene, also 23, suffered a knife wound.
A Naples police spokesman said the group had been on the way back to their hotel when they realised they were being followed.
"Realising the danger they were in, they started to run towards their hotel but the group caught up with them at the corner of Garibaldi Street and Piazza Garibaldi," he said.
"At this point they were attacked with sticks and iron bars."
They tried to take refuge in a hotel but the door was closed.
Trouble had started at about midnight when hardcore Napoli fans - known as Ultras - began throwing items at English fans in a pizzeria.
Three people were arrested over the violence, two from Naples and one from nearly Avellino, Italian police confirmed.
Police recovered an array of weapons - including a baseball bat, aluminium bars with screws protruding and a wooden plank - and Ultra paraphernalia from the home of one man.
"Ultras went out seeking English fans, absolutely," said Filippo Bonfiglio, head of DIGOS, the local department which deals with terrorism and political activity.
"There are groups of violent supporters here in Naples so we could hypothesise something like this would happen but it was impossible to prevent every attack everywhere."
He said there would be about 1,200 police on duty for Thursday's match.
"We are organising more patrols to prevent these kinds of attacks," added Mr Bonfiglio.
"But the city is so great - 1.5million inhabitants - that it is impossible to prevent and control everything."
Liverpool FC responded to the attacks by posting advice on the club's website advising all travellers to "be careful, stick together and heed the safety advice provided with your match ticket".