The Manchester United fan protests against the Glazer family's ownership of the club spilled onto the Old Trafford pitch, eventually forcing Sunday's match against Liverpool to be postponed.
Supporters broke into the stadium and flooded the field as separate demonstrations took place outside the team hotel and the ground. There were clashes outside Old Trafford when police moved in to try to restore order.
"Following discussion between the police, the Premier League, Trafford Council and the clubs, our match against Liverpool has been postponed due to safety and security considerations around the protest today," read a statement from Manchester United.
"Discussions will now take place with the Premier League on a revised date for the fixture."
The meeting of the northwest rivals was scheduled to start at 11:30 a.m. ET. Manchester City would've been crowned Premier League champions if Liverpool won at Old Trafford.
At the peak of the unrest, media members arriving for the match were told the stadium was in lockdown and Sky Sports News reported the match referee was initially turned away from the ground.