It also appears to be a Cooper's hawk to me. Juvenile Coopers tend to be (notice I said tend to be) somewhat more of a problem, because they are young, inexperienced, and generally a bit dumb about what they can handle and what they cannot. They also tend to have less hunting success than adults and might be more prone to try a chicken out of desperation. Generally (key word is generally) an adult Coopers won't mess with adult large fowl chickens unless it is desperate, or too inexperienced to know better. Chicks, adolescents, and bantams are at much higher risk.
A sharp shinned hawk is small enough that it'd be either really desperate or super lucky to mess with adult large fowl chickens. They'd even have a hard time with an adult bantam, but it's not impossible. Chicks are another story.
These are generalizations of course and there are always exceptions, and female hawks are larger and more powerful than the males.