The Butcher's Boy.
Arya Stark and her direwolf Nymeria became involved in a confrontation between Joffrey Baratheon and Mycah, the butcher’s boy. Joffrey had encountered Arya and Mycah practicing sword fighting and became offended when Mycah refused to fight him. Joffrey drew his sword and began threatening Mycah, while Arya tried to stop him.
Seeing Joffrey threatening Arya and Mycah, Nymeria suddenly attacked. The direwolf lunged at Joffrey and bit his arm, forcing him to drop his sword. Arya then picked up the sword and threw it into the river, standing up to Joffrey instead of allowing him to continue bullying Mycah. The incident humiliated Joffrey and left him furious, especially because he had been protected by his status as the prince.
Cersei later demanded that Nymeria be punished, but Arya knew her direwolf would be killed. To protect Nymeria, Arya secretly drove her away into the wilderness. Unfortunately, Robert ordered that a direwolf still be punished, and Sansa’s direwolf, Lady, was killed instead. The event showed how fiercely Arya and Nymeria were connected and became an important early moment in Arya’s journey.