Manchester United's match at home to Liverpool was postponed after fans protesting against the ownership of the club broke into Old Trafford.
Other supporters of the 'Big Six' have staged demonstrations against their owners and/or the club's involvement in the failed Super League, but this was by far the most impactful as it resulted in a Premier League match being called off for the first time due to fan protests.
Here the PA news agency looks at the background to Sunday's events and where things go from here.
Why did it happen?
United fans have, perhaps, been the most vocal of any group in their opposition to the ownership of the Glazer family since the Americans' leveraged takeover in 2005. The tipping points appears to have been the Glazers' leading role in the failed Super League proposal which emerged last month.
What happens next?
The match has to be rescheduled, which is difficult in itself, but protestors are continuing the offensive. Manchester United Supporters Trust have written an open letter to the owners demanding greater fan consultation and involvement to avoid the likelihood of further demonstrations.
What are the implications for United?
The club are likely to face sanctions for the events of Sunday. Fans getting inside the stadium, in addition to the thousands outside, represented a significant enough security threat for the match to be called off. The Football Association will look at the circumstances, after consultation with Greater Manchester Police, the Premier League and both clubs, and could impose a fine, have future matches played behind closed doors when restrictions are lifted or, less likely, a points deduction.
When can the game be replayed?
In a compressed season which already has little room for manoeuvre, the postponement causes a headache for the Premier League as United are due to play every midweek between now and the final day of the season on May 23. The Europa League semi-finalists do, however, currently have a free slot on May 15 – the date of the FA Cup final between Manchester City and Chelsea – but that would mean West Brom v Liverpool being moved to Wednesday May 12, which is the only realistic spare day as the Baggies play on the previous Sunday.
What will be done in the longer term?
In the wake of the Super League plans the Government announced the formal launch of a fan-led review into football governance initially flagged in their 2019 manifesto. The review will be led by former Sports Minister Tracey Crouch. There is a groundswell of opinion to have supporter representation on football club boards and amendments to the rules to prevent seismic changes against the interest of football and its member clubs.