Excellence in Head-Butting
Slate's Explainer evaluates Zidane's headbutt techniques:

Impeccable. Experts in self-defense and mixed martial arts say Zidane's head butt was a flawless demonstration of the form. He positioned his feet close to his opponent and stepped into the blow, contracting his abdominal muscles to curve into the attack. He was also careful to keep his chin down as he approached, which helped him land the strike with the top of his head as opposed to his brow or face.