It happened on July 9th, 2006. The World Cup final was being played between France and Italy, the two teams were tied and Zidane was playing in his last professional match. It was then that the Frenchman headbutted Italy's Marco Materazzi after he had presumably been insulted by the latter throughout the match. Zidane was sent off after a red card and France eventually lost the match.
Materazzi looked back on the 2006 incident
In April, Materazzi took part in an Instagram live chat with Inter supporter Davide Oldani. During the exchange, he opened up about the match 14 years after the fact. He said he has long since stopped resenting Zidane but harbours a nagging grudge against the Italians. He said that Zidane was protected by his countrymen, while he was derided by the Italians, who he said should have defended him.
I am a patriot and I have always defended the colours of Italy. Their criticism is what hurt me the most after the World Cup. They should have kissed the ground I walked on because I scored the equaliser.
This is proof that this match is still very present in the mind of the Italian and that he has not yet made peace with what it represented.