Well, since I assume you can't add lights, you will need to work with the camera settings. A flash isn't going to do you much good unless you can get close enough, and would probably be distracting to the players anyway.
So try the following:
Step 1: Increase the ISO. Depending upon how dark it is, you will likely need to change it to ISO 400 or 800. of course the higher the ISO the more "noise" in your photos, but I really don't think it will be noticeable for you.
Step 2: Switch your camera to Shutter Priority mode (S on the mode dial) and set the shutter speed to at _least_ 125. (Ideally at least 200, but the faster the shutter speed, the smaller the aperture, the less light available). I don't know what length lens you have, but if it is the 80mm kit lens, you should be fine hand holding the camera at a shutter speed of 125. (Anything from 60s and slower will give you camera shake in the photo).
Hope that helps. Sometimes you just don't have enough light. :-(