West Ham co-chairman David Sullivan was struck on his glasses by a coin as supporter unrest marred Saturday's Premier League defeat at home to Burnley, according to Trevor Brooking.
After Ashley Barnes opened the scoring, Chris Wood struck twice to secure a 3-0 win for the visitors at London Stadium, with the second half disrupted by a series of pitch invasions.
West Ham captain Mark Noble tussled with one intruder, shoving him to the ground, while another supporter ran on to the field with the corner flag and attempted to plant it in the centre circle.
Unrest was evident in the London Stadium stands, too, as some home supporters turned their anger on Sullivan and fellow co-chairman David Gold.
Both men were escorted from the directors' box in the closing stages of the match as the atmosphere turned toxic, with television footage showing West Ham icon Brooking sat alone in the area as fans continued to protest against the club's leadership.
And Brooking said Sullivan was hit by a coin during the disturbances, which saw young supporters led to safety on the Burnley substitutes' bench as fighting erupted in the stands.
Brooking acknowledged Barnes' opening goal "triggered problems" and said "there was a quite sizeable group then below the directors' box that came to chant in a really aggressive manner".
Speaking to BBC Sport, Brooking added: "Before the final whistle, two of the directors went upstairs - were asked by the security people to do so.
"I think a coin did hit David Sullivan on his glasses. I didn't see it but I did have that confirmed, which was part of the reason why they thought people in the directors' box should go inside to save any more problems like that.
"I saw some families leaving because the youngsters were frightened. The level of aggression was something I couldn't believe a West Ham fan would get involved in."
After West Ham slipped to a third straight Premier League loss, Noble defended approaching the first pitch invader.
"We are footballers and we are targets but we have got to protect ourselves. A lot of fans got on the pitch," he said.
"In all honesty, a lot of them were running over to where the chairman was sitting but if one approaches me I'm going to defend myself."
West Ham have pledged to launch a "full and thorough" investigation, while the Premier League - who praised the actions of referee Lee Mason and his fellow officials - announced they will also look into the incidents.
The Football Association confirmed it will request West Ham's version of events as the organisation condemned events at the scene of the London 2012 Olympics.
A brief statement read: "The FA strongly condemns the crowd disturbances seen today at West Ham United versus Burnley and will be seeking observations from West Ham as well as awaiting the match referee's report."