MANCHESTER, England (AP) — Police made their first arrest as they worked with Manchester United on Monday to identify the fans involved in violence at Old Trafford during protests that forced the postponement of the game against Liverpool.

The unrest against United’s owners on Sunday saw glass bottles thrown, leading to six police officers being injured, with one receiving a fractured eye socket and another wounded on his face.

“Officers were just trying to do their job and facilitate a peaceful protest,” said Nick Bailey, assistant chief constable at Greater Manchester Police, “however a number of those present became hostile and aggressive towards officers and forced entry to the football grounds, making it very clear that this protest was not peaceful and ruining it for the majority of protesters who had not intended for the protest to become violent.”

The protesters were renewing demands that the owning Glazer family sell United after being enraged by the ill-fated attempt two weeks ago to lead the club into a breakaway European Super League. United could face sanctions from the English Football Association and Premier League over the disorder.

Police did not say what the unnamed 28-year-old man was arrested on suspicion of as it seeks information to identify the protest organizers and those responsible for assaults of the police.

The violence erupted close to when the game was due to kick off on Sunday afternoon as baton-wielding police pushed up against fans throwing glass bottles to disperse the crowd from the concourse outside Old Trafford.

“The majority of our fans have and will condemn criminal damage, along with any violence towards club staff, police or other fans, and these now become a police matter,” United said. “The club has no desire to see peaceful protestors punished, but will work with the police to identify those involved in criminal activity, and will also issue its own sanctions to any season ticket holder or member identified.”

United said speculation floated by the Manchester United Supporters’ Trust that protesters were able to access the stadium through a gate left open by club staff was “completely incorrect.”

“After breaking through barriers and security on the forecourt, some protestors climbed the gates at the end of the Munich tunnel, then forced access to a side door in the stand, before opening an external door that let others through to the concourse area and the pitch,” United said. “A second breach occurred when a protestor smashed the door of a disability access lift, enabling a group to enter the stand.”