Depends on what kind of hawk & what kind of chickens you have. Red Tail Hawks are large enough to kill most any size chicken but "some" do not prefer chicken to eat. Red Tails are not really a danger to big, bold roosters (and I have known of certain roosters of the Game variety killing a Red Tail). A Red Tail would have trouble lifting large fowl and would have to eat it first on the ground (to lighten the carry load).
Cooper's Hawks (aka "Blue Darter," "Chicken Hawk") & Sharp Shinned Hawks, both whose diet are birds, are really only a danger to Bantams or other smaller chickens. Falcons are not really chicken hunters. Broad Wing or Red Shoulder Hawks are not a danger to large fowl breeds as well.
I have Red Tails, Cooper's, Sharp-shinned & Red Shoulder around me and see them several times a week. My chickens seem to know they are "danger" as they hide when they fly over. Only once, a young Cooper's Hawk tried to get my OEGB hen & my big Rooster (9 lbs) ran at the hawk which gave up. I have seen the Red Tails catch & eat squirrels literally in sight of my chickens. Of course, the chickens go bananas upon witnessing the Red Tail swoop, catch and eat the squirrel.