Everton fans invaded the Goodison Park pitch after Premier League safety was securedJurgen Klopp says they are "dangerous", Eddie Howe says they could cause a "tragedy" - pitch invasions and fan violence have dogged English football in recent days as the season reaches its climax.
Since Monday, there have been five pitch invasions, players assaulted, Crystal Palace boss Patrick Vieira clashing with a fan, arrests made and investigations launched.
According to the Football Offences Act 1991, it is an offence for fans to enter the pitch "without lawful authority or lawful excuse".
So why has this happened, what is being said and what will happen next?
What has happened?
On Thursday, Crystal Palace boss Patrick Vieira was involved in an altercation with an Everton supporter during a pitch invasion following his side's Premier League defeat at Goodison ParkOn the same night, Swindon Town players were "physically and verbally abused" after their League Two play-off semi-final defeat by Port ValeThe other League Two semi-final, played on Wednesday, also ended in a pitch invasion with Mansfield boss Nigel Clough saying such incidents are "getting concerning" after his player Jordan Bowery appeared to be shoved by a fan late on in their win at NorthamptonEarlier on Thursday, a fan was jailed after running on to the pitch and headbutting Sheffield United captain Billy Sharp at the end of the Blades' Championship play-off semi-final shootout defeat by Nottingham Forest on Tuesday.On Monday, Luton boss Nathan Jones said Huddersfield supporters were an "absolute disgrace" following their pitch invasion.Swindon forward Harry McKirdy said on Instagram: "I'll take the stick and the songs. But bottles, coins, lighters thrown [at] me, running on and hitting and kicking me/team-mates. Too far."
And his manager Ben Garner said: "I don't know where we're going to as a country, but it's absolutely disgusting."
'We want to avert potential tragedy' - what the managers said
Klopp's Liverpool side could win the Premier League title on Sunday, but he believes celebrations can take place without pitch invasions.
"It could have been dangerous. I'm not sure how you avoid that," he said.
"I don't want to judge. I understand emotions but for the other team it's dangerous. I really hope we learn from that. We should make sure absolutely nothing happens.
"We can celebrate things without threatening ourselves and the opponent."
Newcastle boss Howe, who takes his side to relegation-threatened Burnley on Sunday, said: "I don't mind the celebrational aspect - embracing the success that a team has had is part of football, I've got no issue with that.
"It's the aggression towards the opposition, it's swarms of people around one or two people.
"That doesn't sit well with me at all, that's something [on which] we have to act very quickly because we want to avert potential tragedy."
Why has this been happening?
The pitch invasions have come at the end of the first full season with fans present in stadiums since the start of the Covid-19 pandemic in March 2020.
Geoff Pearson, a professor of law at the University of Manchester who researches crowd behaviour, said the effects of the lockdowns has caused a "deterioration in the behaviour of some fans", adding this has affected the relationship with fans and police, who "rely on knowing who the fans are, including the potential troublemakers, and all those opportunities during the pandemic dried up".
He told BBC Radio 5 Live: "Once we had the first major pitch invasion then there is a certain element of copycat, because there is a certain element of fans wanting to be seen as authentic.
"That's one of the real challenges - what is authentic fan behaviour?
"Unfortunately, at the moment, running on to the pitch, setting off smoke bombs, is what is seen as what authentic fans are doing."
In February, the national lead for football policing, chief constable Mark Roberts, said cocaine use is helping to drive a rise in disorder at matches.
On Thursday, the government announced anyone caught in possession of or supplying class A drugs in connection with football faces a five-year ban and their passport being taken off them.
Police data released to BBC Sport in January showed arrests at football matches across the top five English leagues are at their highest levels in years.
What have others said?
After the incident involving Sharp, the Professional Footballers' Association called for a review into matchday security and fan disorder, which was later echoed by Preston North End manager Ryan Lowe.
He said the violence seen this week in football is "disgusting" and "bizarre".
"Fortunately it'll get stopped for next season for the simple reason that Billy Sharp has had to take the nut from some idiot, got stiches in his face, because it could have possibly killed the lad. It cannot happen ever again," he said.
"Who is to say Billy Sharp wouldn't have banged his head and never woke up?"
Writing on social media, Accrington Stanley chairman Andy Holt said it is a "disaster", adding: "You win, you draw, you lose. If you can't cope with that STAY AWAY.
"You're ruining the day for many, increasing club security cost and as a result ticket prices for all. I'm not paying extra costs because of these stumps.
"If costs go up, tickets go up. Ban them all, jail them all, we don't need them in football."
However, Everton boss Frank Lampard doesn't see pitch invasions as an issue - so long as fans behave.
"If it is done in the right way let them stay on the pitch, let them have their moment," he said. "As long as they behave, no problem."
What happens now?
As the fan who headbutted Sharp has discovered, the repercussions of such behaviour can be severe. He has been jailed for 24 weeks, fined and given a 10-year football banning order.
In March, an Everton fan who threw a plastic bottle at Aston Villa players celebrating a goal in their Premier League meeting in January was given a suspended prison sentence.
Pearson believes "a lot of legal action will have to be taken against a lot of people" in the close season as fans, particularly those who have been involved in violence during the pitch invasions, are identified.
Those issued with football banning orders are prevented from attending games for at least three years, and can be asked to surrender their passport to ensure they do not travel to matches abroad. Those who breach the orders face six months in prison.
The Premier League, EFL and clubs are receiving advice from the Crown Prosecution Service on how to build the strongest cases possible against fans who attack players.
On Wednesday, the EFL said it was to "consider what further measures are now at our disposal" in order to tackle crowd behaviour.
The FA does have the power to order ground closures - either full or partial - for issues involving supporters, while fines have previously been issued to clubs.
The two most significant fines in recent times were West Ham being fined £100,000 when fans went on to the pitch during a game against Burnley at London Stadium in 2018, and Aston Villa being fined £200,000 in 2015 when their fans repeatedly went on to the pitch during an FA Cup tie with West Brom at The Hawthorns.
Birmingham were fined £42,500 when a fan went on to the pitch and punched then Aston Villa player Jack Grealish during a derby game at St Andrews in March 2019.
