Sports photography is one of the more rewarding types of photography. It is more challenging to master than it looks as things are usually happening really fast, which leaves little time to think about composition or technical aspects. Most other types of photography happens at a relaxed pace and allows you to plan and think about your shot.
Equipment Guidelines
Sports photography is very demanding on your wallet. If you want to get good at sports photography be prepared to start spending some money. Sports photography lends itself to favor fast telephoto lenses, ultra wide angle lenses, and the fastest camera you can buy. You'll need to invest in at least one or two fast telephoto lenses and at least one wide angle or ultra wide angle lens. When it comes to camera bodies, professional sports photographers prefer the Canon EOS 1D or Nikon's D2X which are top of the line sports cameras.
You don't need to invest in top of the line DSLRs though; a mid level camera that can shoot at 5 frames per second and has relatively fast auto focus capabilities is more than adequate if you couple it with a pro level lens - think Canon EOS 30D or a Nikon D200 coupled with a 300mm or 400mm f2.8.
Canon EF 300mm f2.8L. At $3900 dollars this lens is not cheap, but it's one of the sharpest and fastest telephoto lenses I have used to date.