Family and friends of West Ham players were attacked by rival supporters after a match in the Netherlands.
AZ Alkmaar fans broke through a fence and attacked visitors sat in a reserved section following the final whistle in the Europa Conference League semi-final.
A brawl ensued – and several West Ham players, including captain Declan Rice, tried to intervene.
Police and stewards were quickly on the scene to prevent further confrontation and calm was restored 10 minutes later.
West Ham manager David Moyes admitted that his players were angry following the incident.
He told BT Sport: “We’ll need to wait for the dust to settle to see what it is but the biggest problem is that is the area where the players have all their families in, friends and family.
“That is where the problem came and a lot of players were getting angry because they couldn’t get to see if they were okay. But look, I don’t know. We’ll have to wait and ask the officials what really happened.”