Ulrich von Gradwitz meets Georg Znaeym in the forest, and as soon as he sees him, he is ready to kill him.
Explanation:
They both hate each other since they were children, and that hate became so strong that they have come to the pint of killing each other.
The story of the hate of them derives from the past where the reason was jealousy, as some proofs say. Ulrich's family was rich and they have won disputed lands, which made the Znaeym family very jealous.