He lost control under repeated insults coming from the Italian footballer.
Ah, poor man................someone says a few things to you and all self control disappears..........
Anyway, quoting from the BBC website:
Materazzi defended himself on Tuesday in the Italian newspaper La Gazetta dello Sport, when he said: "It was the kind of insult you will hear dozens of times and just slips out of the ground."
"I did not bring up Zidane's mother; for me a mother is sacred."
Materazzi and Zidane became involved in a verbal spat with 10 minutes to go in extra-time with France and Italy drawing 1-1 in the World Cup final.
After Materazzi's insult Zidane shoved his head into the Italian's chest and was sent off, with Italy going on to win the match 5-3 on penalties.
"I held his shirt, for only a few seconds," said Materazzi, who had scored Italy's equaliser after Zidane put France ahead from the penalty spot.
"He turned towards me and scoffed at me, looking at me with super arrogance, up and down.
"He said 'if you really want my shirt, you can have it later.'
"It's true, I shot back with an insult."
BBC Radio Five Live asked for help from a deaf lip reader, Jessica Rees, who read the words phonetically to an Italian translator.
She deciphered the insult as being "you're the son of a terrorist whore" - a translation also carried by many national newspapers in Britain on Tuesday.
The BBC's Ten O'Clock News also called in experts to study the television footage of the incident and determined the following:
Materazzi's first word to Zidane was "no" before he then told him to "calm down".
He then accused him of being a "liar" and wished "an ugly death to you and your family" on the day the Frenchman's mother had been taken to hospital ill. This was followed by "Go f*** yourself".
Anyway, it's well known Italian players spend the whole game lying and cheating, so we can discount his version, can't we?