A good attempt, I appreciate also what you are trying to do, as a gesture and a concept this drawing works. Anatomically the right arm seems to be a little long. If you stand Cap up, it seems as if that arm would hang way below where it should. The pose is also a good attempt at a battle ready pose, but doesnt feel natural, it needs to be more dynamic. I have to believe that the Avengers would follow this man into an army of Ultrons. Also from a comic geeks point of view, Caps' shield has two straps on it, not one. :)