Hawks versus small birds

Today, I noticed a terrorist act. However, instead of among people- this was among birds.

Five small birds were ganging up on one large hawk. Surrounding and dive-bombing mid-flight. The hawk was making an attempt to fly out of the way. Why was this going on. I think it's an issue of territory, (food, resources, etc) As in: That hawk might have had a history of disrupting the small birds. Then, the little birds decided to band together and chase the hawk out. Either way, it was reminiscent of a dogfight (which is a form of aerial combat between fighter aircraft- up close and personal).