70-200 vr

I just purchased a 70-200 vr lens ifor my D80 in order to take pictures of my boys in sports. I took some in an indoor gym last weekend and was disappointed in the results. I set the aperature to 2.8 to allow for the most light as possible. However, many of the action shots came out a little fuzzy. How should I set my camera for these shots? It was on auto-focus. I was having trouble focusing on the action. When I set the shutter speed to a faster level, the pictures were too dark.

I am pretty much a beginner and need some advise.