What is significant about the fact the Sohrab is the one who stops Assef? How is it accomplished?

Sohrab tells everyone to stop. Our fighters look up. Sohrab has placed a brass ball from the table in his slingshot. (It sounds hefty and substantial.) After some useless commands to Sohrab, Assef gets his due. Sohrab lets fly and the brass ball smashes into Assef's left eye. This is the same eye Hassan threatened to blacken all those years ago. Like father, like son – or something.

•Sohrab and Amir peace out. They hop in Farid's car and they're off.