For many of you, this was the reason you bought your first DSLR. Shooting sports is really fun, and even more so if it's your own kid. This last fall, I spent a fair bit of time shooting high school sports for the youth in a little Boy Scout group where I volunteer. I figured out a few things last fall that I think will help you to improve your sports photos.
Whether you shoot peewee football or high school track and field, the biggest struggle you'll have is probably the background. These sporting events are generally not held in professional sports stadiums. In fact, most of these games occur in a park or at a school, so the background is often a neighborhood surrounding the park or school. Even if you get everything else right when photographing the sport, if the background is random buildings, the shot will most likely look like a snapshot. This is all part of simplifying your composition.
So what can you do? Bring a step stool or stand on something high like the bleachers. By elevating your position, you'll be shooting down on the athletes. This makes the grass the background rather than the ugly neighborhood, telephone wires, or your tan minivan over in the parking lot. Simplifying the background in this way will drastically improve your shots.
Using a step stool is perfect for sports where the athlete is looking up, such as javelin, discus, shotput, shooting free throws, when a swimmer comes up for a breath, etc. However, this method doesn't work well for sports where the athletes commonly look down to the ground, such as soccer, running events in track, wrestling, etc. For this type of situation, you'll need to plaster yourself on the ground for hours on end.
By getting as low to the ground as possible, the sky becomes be background, which is much more natural and clean than the typical distracting background. Also, remember that the angle will improve the closer you get to the athletes. If you're shooting the athletes from 100 yards aways, you probably won't be able to tell whether you're crouching down low.
If you're stuck with distracting backgrounds, you'll have to use depth of field to blur out the background as much as possible. Unfortunately, if you're shooting a cheap telephoto lens whose maximum aperture when zoomed out is f/5.6, it can be tough to get as much blur on the background as possible. But, remember from the post last week that aperture is not the only thing that affects depth of field.