West Ham players dived into the crowd to protect their families after they were ambushed by Dutch hooligans.
As substitute Pablo Fornals' stoppage time winner booked the Hammers' place in the Europa Conference League final, dozens of Alkmaar ultras rushed along the 'dead' zone at the front of the stand to attack the players' celebrating contingent.
The shocking scenes, a throwback to the hooligan dark ages, took the gloss off West Ham's first passage to a major final since 2006 and a first in Europe for 47 years.
