In the book "The Kite Runner" the fight between Assef and Amir has been coming for many years. Years before Assef had raped Hassan, Amir's friend and unbeknownst to him at the time, half-brother. Assef was a bully and a sadest. He tormented the children in the neighborhood including Amir. Hassan had always stood up for Amir, but Amir did not return the favor when Hassan needed him. Amir had spent his life as an insominac over the situation.
WhenAmir goes to get Hassan's son, he is confronted by Assef who has control of the boy. Sohrab has his father's face and skin. When Amir sees him he is brought back to the memory of the boy's father. The boy is dressed like a girl and he places his hands around the boy and makes the boy dance. In this way the boy is a symbol of what had happened to his father at Assef's hands. Assef means his actions as a slap in the face to Amir.
The confrontation is a symbol as well since it represents the stand that Amir finally takes. His father Baba had tried to get his son to have courage and take a stand. Assef makes Amir fight for the boy. It is the fight that was meant to happen many years before.
Assef puts on brass knuckles and begins to beat Amir. However, instead of Amir panicking or crying he starts laughing. He realizes it was meant to happen. The fight i some way symbolizes the punishment he must take for not having helped Hassan.
Sohab pulls out his slingshot and puts a brass ball in it. The boy shoots his tormentor in the eye. Assef falls to the floor screaming, but he has the music playing and can not be heard. The boy and Amir escape. Sohab's protection of Amir symbolizes the protection that his father had also provided Amir.
Amir is left with a scar on his lip. His lip is split which also symbolizes the split (hare lip) of Hassan's that had to be repaired. He has faced his fears and let go of his guilt and shame.