Looking at the difference in wattle / comb development (compared to the others) it could be a rooster but its difficult for me to tell as the hackle feathers are difficult to pick out, and the photo does not show the saddle feathers. Are its legs thicker than its siblings?
Having said all that, if its is crouching when you approach - it means its a hen and wants to be mated. The wattle / comb development may suggest that it is reaching maturity.
If there is not even an attempt at a crow when you let it out of the coop in the morning, this further supports the pullet theory.
See what other more experienced members think, but, as i say, if it is crouching when you approach it, its for sure a girl!
CT