AZ Alkmaar have been fined £68,770 after their supporters tried to storm an area in which West Ham players' friends and family were seated during their Europa Conference League clash in May.
The Dutch side were also ordered to play one UEFA competition match behind closed doors - though that sanction has been suspended for two years.
Violence broke out at the AFAS Stadion in the Netherlands, after Pablo Fornals' stoppage time goal gave the Hammers a 3-1 aggregate lead in the second leg of the semi final on May 18.
Hammers supporter Chris Knoll - better known as Knollsy - went viral in the aftermath from clips of him fighting Dutch ultras single-handedly.