Perceval, who knew from the blow he had received that he who had delivered it was a knight of great strength, took his sword, for he saw clearly that he could not get away without a struggle. When he had drawn it from its scabbard, he headed toward the knight and gave him a blow on the helmet so violent, putting all his strength into it, that the other man could not stay in the saddle but fell to the ground so stunned and dazed that he did not know if it was day or night.

Post-Vulgate Quest for the Holy Grail