If you are going to be changing between a moving target and one that is still, you should consider using the 3D-tracking AF mode. This mode mixes both the AF-S and dynamic modes for shooting a subject that goes from stationary to moving without having to adjust your focus mode.
When you have a stationary subject, simply place your selected focus point on your subject and the camera will focus on it. If your subject begins to move out of focus, the camera will track the movement, keeping a sharp focus.
For example, suppose you are shooting a football game. The quarterback has brought the team to the line and he is standing behind the center, waiting for the ball to be hiked. If you are using the 3D-tracking AF mode, you can place your focus point on the quarterback and start taking pictures of him as he stands at the line. As soon as the ball is hiked and the action starts, the camera will switch to tracking mode and follow his movement within the frame. This can be a little tricky at first, but once you master it, it will make your action shooting effortless.
To select 3D-tracking, simply follow the same steps listed for selecting dynamic modes but instead select the 3D-tracking mode. It is important to know that the 3D-tracking AF mode uses color and contrast to locate and then follow the subject, so this mode might be less effective when everything is similar in tone or color.
Choosing a focus mode
Selecting the proper focus mode depends largely on what type of subject you are photographing. Single Point is typically best for stationary subjects. It allows you to determine exactly where you want your focus to be and then recompose your image while holding the focus in place. If you are taking pictures of an active subject who is moving quickly, trying to set a focus point with Single Point can be difficult, if not impossible. This is when you will want to rely on the Dynamic Area and 3D-tracking modes to quickly assess the subject distance and set your lens focus. This can be especially helpful if the subject distance is varying constantly.