Captured with continuous auto-focus mode.
On digital SLRs, there are multiple options for nailing your focus. You can use full-manual, giving you control over selecting what is in focus, and adjusting the focus. Single-Auto, which focuses for you based on the focus point you select. And Continuous-Auto where the camera continuously adjusts focus to maintain sharp focus on a moving subject. Some lenses will also have an adjustment for auto and manual.
Many photographers prefer different focusing techniques, but mine have served me well so far, so here they are. For sport's photos where the athlete is continually moving closer to me, I prefer continuous auto-focus. You will need to select a focus point using your directional wheel on your camera. Some cameras also have 3d tracking modes which will follow moving objects for you. With Nikon you can go into your autofocus menus and change your focus lock-on time. I prefer short for a shot like this so that the camera can capture more in-focus images. If the athlete is moving slowly, you can use a longer lag time to guarantee that each shot is in focus. The reason not to use this when the athlete is coming at you quick, is that the distance is changing so rapidly the camera will not be able to lock-on, and therefore not capture an image.
When the athlete/subject is moving perpendicular to the lens, I will use single-point autofocus on a spot the subject will go through, and establish my focus in advance. Then I simply move the switch on either the camera or lens to manual, and fire away. If you prefer manual from the start, this will work equally as well. This way your camera is never changing focus. Remember though, that this will only work if the subject is always the same distance from the lens.
Captured with pre-set single auto-focus, then flipped to manual to lock setting in.
If the subject were jumping off of a cliff or skiing past a certain tree, and I only wanted ONE image, I would pre-set my focus like described above on the key image point. This makes sure that I will have an in-focus sharp image EXACTLY where I want it.
If I am capturing images of a non-moving subject, I will use single auto-focus to guarantee a sharp image. I enjoy manual focus, but sometimes I feel it's more accurate to use the auto-focus. There are also different AF selection modes including "dynamic" and "singular". I generally leave mine on "dynamic" but will describe these more in a future post.