In the 110th minute of the 2006 World Cup final against Italy, Zidane was sent off for headbutting Marco Materazzi in the chest in an off the ball incident. The two players exchanged words before Zidane began to walk away from him. Materazzi then said something to Zidane, who turned around, made a run-up and head-butted Materazzi in the chest, sending him to the ground.
These are some points of view about this subject :
as seen by the French
as seen by the Italians
as reported by the press
You can find the entire gallery here.