Why do amir and Farid go to the Ghazi Stadium? What atrocity do they witness while there?

The following day they go to the soccer game at Ghazi Stadium. The field is just dirt, and the crowd is careful not to cheer too loudly. At halftime, Taliban in red pickups drive into the stadium. They unload a blindfolded man from one truck and a blindfolded woman from the other and bury each up to the chest in a hole on the field. The woman is screaming uncontrollably.

A cleric on the field recites a prayer from the Koran and announces that they are there to carry out God’s law. When adulterers throw stones at the house of God, he shouts, they must answer by throwing stones back. Another man steps out of a pickup, and Farid and Amir see it is the official they are looking for. He is wearing black sunglasses, as Zaman said. The official throws stones at the head of the man in the hole until his head is a bloody pulp and his chin hangs to his chest. Then he does the same to the woman. They pile the bodies into the back of a truck, and the second half of the soccer game begins. Farid tells one of the Taliban nearby that he has personal business with the official, and the official agrees to see them that afternoon.