iso 1600, use spot metering, and central AF, use A priority with the fastest possible aperture
I agree with Adamz on this. But I would like to say why.
Set ISO to 1600, as it will give you moderately high noise, but the fastest possible shutter speed to stop action. After you get some experience with this ISO, you can decide if it is OK, or you need 800, or even could afford more noise and go to 3200. But 1600 is a good starting point, and near the highest you can go, so near the fastest shutter speed you will get.
Set the Mode to A, and use maximum aperture. This is just insuring that the lens is open as far as possible. It gives you the most light, but will need focusing to be good. At this point you are taking control of the camera, and only that way can you judge how to improve what you are doing, IMHO.
Set metering to spot metering, so you get the proper exposure of the person, ignore the rest of the scene. Here, I would shoot a few photos of the person you are interested in, and check exposure of the result. If it is not good, then you have to figure out why, such as the lighting issue jonnyapple mentioned. Do this during idle time of the game.
Use central AF. With known good settings the give proper exposure, already checked per above, the number of tasks has been reduced to figuring out where the action will be, and getting focus there. Per Adamz method, you already have set the camera to get the highest shutter speed (other than using 3200 ISO) to stop action.
I think until you have done these things, and gotten the best results you can with this lens, it is not time to think about some other lens.
That's my 2 cents as a newbie DSLR operator.