The Alkmaar side's head coach ordered his players off the pitch after the ref dismissed his goalkeeper following a fight with a 'fan'
An Ajax fan entered the pitch after 38 minutes of play and ran toward AZ goalkeeper Esteban before aiming a karate kick at the Costa Rican.
The AZ shot stopper reacted by kicking his attacker to the ground, before onrushing stewards intervened and took the Ajax supporter away.
Referee Bas Nijhuis consequently showed the attacked AZ glovesman a straight red card for misconduct, much to the dismay of AZ coach Gertjan Verbeek.
The Alkmaar side's trainer entered the pitch and ordered his players to leave the pitch and head for the dressing rooms.
"We must await reports from Ajax, AZ, referee Bas Nijhuis and KNVB-observer towards the prosecutor of the KNVB," KNVB director Bert van Oostveen said.
"He will investigate this case and we will see if there's a guilty party. After that there will be a decision about how and if the match will be continued. We will know more around Christmas."