West Ham manager David Moyes admitted he was concerned for the safety of his family after AZ Alkmaar hooligans attacked Hammers fans following Thursday's Europa Conference League semifinal in the Netherlands.
Pablo Fornals' stoppage-time goal sealed a 1-0 victory that booked West Ham's first European final appearance for 47 years.
But the semifinal second leg was marred by ugly scenes when a gang of black-shirted, hooded AZ fans attempted to storm into the area reserved for friends and family of the West Ham players and management.
West Ham stars including Michail Antonio, Said Benrahma, Aaron Cresswell and Flynn Downes climbed over the advertising hoardings in a bid to stop the trouble.
Moyes, whose 87-year-old father was at the match, said: "I can't explain what happened and why it happened.
"I can only say the players were involved because it was the family section and most of their family and friends were in there. That was probably the reason for the reaction.
"Was I worried? Yeah, my family were there and I had friends in that section. You're hoping they would try and get themselves away from it.
"I didn't recognise it because I'd gone onto the pitch. Security wanted to take me inside, but I had to make sure my players weren't involved.
"What we don't want to do is in any way blight the night because it certainly wasn't West Ham supporters looking for trouble. Hopefully they'll look into it."
'VERY UNFORTUNATE'
There was widespread video of the incidents on social media, with images also shared of clashes between rivals fans earlier in the day on the streets of Alkmaar.
During last week's first leg at the London Stadium, won 2-1 by West Ham, members of AZ players' families were involved in a confrontation with fans of the east London club.
"When families or friends are coming to the stadium we don't want to see things like that," Hammers goalkeeper Alphonse Areola said.
"They want to enjoy the event and we want to enjoy it with them as well. We were worried about them."
Uefa, European football's governing body is expected to launch an investigation into the trouble, with Dutch police saying there have been no arrests yet.
"So far, no arrests have been made. Our aim was to disperse the crowd and restore order as quickly as possible, in which we succeeded. The police will investigate footage of the incidents and try to identify supporters. Arrests may follow from this," local police statement said.
"Together with AZ, the municipality of Alkmaar and the public prosecution service we will evaluate last night's incidents, which we regret having happened. This kind of behaviour has no place in football."
Uefa will wait for the relevant reports before deciding on any action, but AZ could face heavy sanctions.
AZ boss Pascal Jansen added: "What happened last week was very unfortunate and then you get the same feeling as what happened tonight.
"I feel a little bit ashamed it happened in our stadium but you have to control your emotions."