Lens recommendataion: Fast AF for indoor sports?

You're getting a lot of mixed information here including sample pictures that while excellent are completely irrelevant to your original question.  The biggest challenge in shooting sports in a HS gym is going to be the lack of light and the movements of your subject!

You're going to need SS >= 1/500 to get anything worthwhile.  In order to do that with a 2.8 zoom you're going to need ISO of 3200 or more which may be OK depending on how your pp skills with noise reduction or how your camera handles noise.  There's no perfect solution for this kind of shooting.

You can get sal 50f1.8 for less than $200 and test outcome shooting at f2 iso 1600. If the gym you'll be shooting at has enough light then a 50-150 2.8 or 70-200 2.8 would make sense.

Take lots of shots as the keepers may be few and the film is free 

--
dancph