The fan ran on and seemed to have a little jump and kick at the goalkeeper. It turns out this was really stupid idea. Remember all goalkeepers are mental, especially South American (Central American) ones. AZ's Costa Rican goalkeeper Esteban Alvarado went ape shit and repeatedly put the boot into the fan who had fallen over.
A red card was awarded to the goalkeeper, which seems like a fair thing to do. Although I'm not too sure what the rules are when it comes to kicking a fan. It's either a red card or an assault charge. What I don't understand is why they abandoned the game after the incident? It's almost as if they are saying, "we had to send you off but we appreciate your work".
The Dutch FA said it would be unreasonable to expect them to play on with 10 men. Therefore the game will be replayed behind closed doors, presumably for fear of the goalkeeper going on a John Rambo style rampage but without the heavy artillery. Instead of a machine gun, he will go charging through the stadium kicking the head off any Ajax fan that dares get in his way.