As you can see now by the other answers, it's pretty much about how much light you can get in and how fast !!
That's what all the talk is about on other threads.
You are up against a VERY tough situation. Someone suggested a 50mm f1.8 lens. That is a good choice for a couple of reasons. It is not the most rugged lens because of the plastic construction, however,most importantly it is FAST and is a very sharp lens. The cost is reasonable also.
Punch up your ISO to 1600 (granted you will get more noise) but you will get a stop or two more. You can clean it up some in post processing.
The lighting coloris a nightmare. If you try to add your internal (built in) flash, you create more problems to an already tough situation.
I would get as close to one of the strongest light sources and stay there. Get as close as you can to the action. If you get the 50mm lens (above) you will do your zooming with your feet as it is a prime lens.
Sometimes the competitors will do there stuff in front of where the cameras are. Everybody likes to "showoff".
Remember its all about Light !!
Good luck and please come back with your experiences - we want to know how it went.
Good luck and Good shooting.