This happens in chapter 7-8 and is after Hassan has been raped and Amir didn't do anything to stop it. Amir throws pomagranates at Hassan and wants him to throw them back at him. He taunts him to do so and even calls the Hazara boy a coward. When Hassan continues to remain silent, Amir hits him with another one and another one until Hassan is smeared in red like he’d been shot by a firing squad.
Finally, Hassan picks up a pomegranate and Amir thinks he’s finally going to hit him. But Hassan instead smashes the fruit against his own forehead and asks Amir, “Are you satisfied? Do you feel better?” He turns away and walks down the hill while Amir once again breaks into tears and asks himself, “What am I going to do with you, Hassan?” The answer occurs to him only as he, too, is walking back toward home.