The main issue is that hawks, like most birds of prey, are ambush predators. Sharp talons and beak, aside.. they aren't really equipped physically for fighting. They don't have the physical strength or flexibility for it. Yes, the rooster is doomed... unless the hawk misses that initial attack. Then the playing ground is leveled. Once the hawk looses the elements of speed and surprise (which is the stoop and dive then impact), those are its most powerful weapons gone. If it lands in an awkward spot, like the ground or a low hanging branch.. or worse, under an overhang, a brave rooster can take it on with a decent chance of winning.