Tensions at West Ham reached a boiling point as fans invaded the pitch and others vented their anger at the board during a 3-0 Premier League defeat to Burnley at the London Stadium.
A turbulent week off the pitch -- which has seen fans cancel a planned protest march and then turn against each other when a second demonstration was arranged and subsequently shelved -- became toxic.
Ashley Barnes had put Burnley ahead early in the second half when a fan ran into the middle of the pitch, left unchallenged until Hammers captain Mark Noble intervened and shoved the man to the ground.
As that fan ran back toward the stands, another two came on and were eventually led away by defender James Collins.
Burnley's second goal, scored by Chris Wood, proved the final straw for hundreds of fans who charged along the concourse between the tiers of the stadium and gathered under the directors' box to chant: "Sack the board" and "You destroyed our club."
Joint-owners David Gold and David Sullivan, whose decision to move the club from their old Upton Park home to the former Olympic Stadium is behind the anger, were reported to have left their seats for their own safety.
A fourth supporter, meanwhile, picked up a corner flag, ran to the centre circle and planted it in the ground.
Police were then positioned along the touchline and specifically around the West Ham bench, where more disturbances appeared to take place.
The Premier League issued a statement condemning the scenes.
"It is essential that everybody who plays or attends a Premier League football match can do so safely," the statement said.
"There is no place at any level of the game for what happened at the London Stadium today.
"While the official investigation of the incidents will be carried out by the Football Association, we will be asking our own questions of West Ham United about what happened this afternoon, especially to ensure similar events never reoccur.
"We would like to commend referee Lee Mason and his team of officials for their actions which, combined with the cooperation of players and coaching staff from both clubs, enabled the match to be completed."
West Ham vowed to take "decisive and appropriate action'' after an investigation.
A club statement said: "West Ham United have immediately launched a full and thorough investigation into the incidents which marred the second half of today's match and are committed to taking decisive and appropriate action.
"An emergency meeting has been called with all London Stadium stakeholders. There will be no further comment at this time.''
West Ham manager David Moyes urged fans to get behind the team.
"We want the supporters behind us, but you can't cross the line and come onto the pitch," he told Sky Sports.
"I don't think I've been at football games in my time where I've seen that. All I'll say to all of them is that we need them.
"We're fighting for points. We're all in it. The players know we did well today for long periods. We didn't do so well for a couple of minutes in the second half. We needed the supporters with us in a different way.
"All I ask for is that everybody sticks together and we try to get ourselves enough points to make sure we're a Premier League team [next season]."
There had been little sign of what was to come as the match kicked off, however.
A smattering of supporters had trooped along the proposed protest route, while in the stadium the mood was more apathy than antipathy.
There was a minute of applause in memory of the 25th anniversary of the death of Bobby Moore, with a mosaic in the crowd bearing his name and shirt number.
But things changed after a first half West Ham dominated, with Nick Pope making decent saves to deny Marko Arnautovic and Manuel Lanzini.
As the wheels began to come off, the anger toward the board grew and problems began to break out on the pitch and in the stands.