AZ Alkmaar goalkeeper Esteban feared the pitch invader who attacked him during the KNVB Beker clash at Ajax may have been carrying a knife.

The Costa Rican was confronted by the 19-year-old, who was arrested, after 37 minutes of the contest at the Amsterdam ArenA but fought him off before kicking him twice as he lay on the turf.

Some critics have questioned the aggression used by Esteban but he insists he was acting in self-defence and driven by fear.

He told reporters in his homeland: "I was very scared.

"The first thing I thought was that he had a knife. I thought only to defend myself. I was afraid he might be armed.

"To anyone who thinks I was overly aggressive, I invite them to experience what I experienced and then judge.

"I have children, brothers, a father and mother and I don't know if the person coming towards me is going to give me a kiss or cut me in half.

"I am not proud of what I did but I just did what anyone else would do but these people must learn they cannot get away with it."

Esteban, 22, was sent off for his part in the incident, prompting furious AZ coach Gertjan Verbeek to take his players from the field and the game to be abandoned with Ajax leading 1-0.

The KNVB have subsequently rescinded the player's red card but not yet ruled whether the tie should be replayed or resume from the 37th minute.

Esteban revealed he had received messages of support from Ajax, but believes the Amsterdam club were not to blame.

"Frank de Boer has apologised as have a few of the players but I told them they did not have to be ashamed of an idiot," he said.