Several Manchester United fans attacked Brentford supporters before the two sides met on Monday.
Video footage shows United fans rushing towards the Bees fans as they made their way towards the visitors' entrance at Old Trafford before kick-off.
Missiles were launched, punches thrown and flares set off in distasteful scenes amid an angry atmosphere, with widespread frustration at the deeply unpopular Glazer family that owns the club.
Riot police were forced to intervene to prevent the clashes between the fans spilling over into outright violence.