Sports are probably one of the greatest inventions of the human race. They have always attracted attention of the public; thus, when photography came along, they began to attract photographers as well. Action, emotions, spectacular episodes - these are the things that most photographers look for in a sporting event, doesn't matter if it's a school softball game or a big league match-up.
Of course, a professional sports photographer has many advantages over an amateur shooter. One of them, which is probably the most important, is equipment choice. There's no need to say that professional equipment is extremely expensive. Most photographers that take pictures of sport events professionally use top-of-the-line 35 mm SLR cameras with fast, super-long telephoto lenses. All this equipment actually lets them to shoot from any location of the field/stadium. Above that, they have deep knowledge about the kind of sports they are specialized in and about its main players.
If you're just an average photographer, you might think that it is impossible for you to take a picture of the same quality with those that professional sports shooters take. However, with some simpler than professional equipment you actually can take rather decent photos on local sports events where you can get closer to the field or other place of action. All you're going to need is fast, medium telephoto lens or a fast, quality zoom lens that ranges from around 80 mm to 200 mm or more. These must let you achieve sufficient quality of your pictures. Just take some practice in your techniques and in choosing a good angle; that will help you a lot.
In fact, positioning is one of the most important factors in sports photography. It will not only allow you to take great pictures and capture extreme moments, but also will make the light work for you. Of course, choosing a good position is impossible without knowing the game in depth, seeing all its hidden parts and predicting what's going to happen next. Only a person that loves both the game and the photography can make really excellent sports pictures.