"Despite his enormous physical disadvantage, Oberyn using speed manages to wound Clegane several times and cripple him by finding сhinks in his armour and severing his hamstring after the Mountain tired from chasing him. As Oberyn approaches Gregor to finish him, the prostrated Clegane grabs hold of Oberyn and smashes his armoured fist into Oberyn's face, killing him: dashing out his brains after first destroying his teeth and knocking out his eyes.
"