The game, which took place at the Amsterdam Arena, was rudely interrupted by a 19-year-old drunken yob in the 36th minute.
The "supporter" ran towards Alvarado but was unsuccessful in his attempt to land a kick, before falling to the ground. The Costa Rican
began to unleash several hard kicks to the bald-headed man, before stewards rushed onto the pitch to escort him away.
Referee Bas Nijhuis wasted no time in showing Alvarado a red card, despite large protests from his team-mates and manager Gertjan Verbeek.
According to the Daily Mail
, Nijhuis said: "I understand that Esteban was defending himself, but he walked to him (the supporter) and kicked him multiple times. He could also have walked away."
As reported by the Telegraph
, Ajax director Jeroen Slop said: "This was a terrible incident and we deeply regret it and offer our sincere apologies. The supporter has been handed over to the police.
"It was a 19-year-old man who was probably under the influence of alcohol. He said he hated the AZ goalkeeper and had therefore attacked him."
Ajax were leading 1-0 at the time of the incident, although it's unknown whether or not the game will be replayed, according to Bert van Oostveen – director of the Dutch Football Association.