I'll give you an example. At Ensworth, when we run, say, a 5 yard hitch, we are advised to pump our arms when we come to a stop and keep our eyes up. This is done to confuse the defender. If you start looking down at the ground, or if you're running and suddenly stop your arms, the defender can look at you and be able to tell that you are about to stop and turn around. When he sees this, he can jump your route and will at least tackle you right away if he doesn't pick the ball off. If you keep your eyes forward and your arms moving, it is much more difficult for him to anticipate the route like that. There are little nuances like this one to every route, whether it be head fakes, false steps, or other things like that. These little nuances make it harder for the defender to predict what you are doing and, therefore, makes it harder to defend you. These little things get you more open, but most players (and their coaches, until they get to college) do not focus enough on it. Who wants to practice stopping on a hitch route when you could be practicing highlight-reel catches?