In chapter six, it is winter. This is one of the favorite times for the boys, as they have time off from school and more importantly they are able to fly their kites. It is particularly special, because it is time for the kite fighting tournament. Amir is excited to enter the tournament. Baba also takes the boys to a kite maker and he buys them kites.
In chapter seven, as the tournament approaches, there is a sense of excitement. Amir believes that he has a chance to win. Amir does extremely well as his kite is one of the last two flying and in the end, he wins. Hassan, at this point, runs to chase down the fallen kite. In this culture, it is a mark of honor to gain the last fallen kite. Moreover, Hassan is considered the best kite runner.
Hassan goes off in search for the kite. However, he is surrounded by a group of boys would also want to kite, but he would not give it. They beat him down and rape him. Amir sees this, but does nothing. Fifteen minutes later, Hassan comes out bleeding and the boys never mention this incident again.
This is one of the pivotal chapters in the whole book, as this imagery stays with Amir and fills him with guilt his whole life. It defines him and he needs to be set free, which he does as he faces this weakness as an adult. To get a sense of the importance of the scene, all one needs to do is to look at the title of the book.