For indoor sports, the Tamron or Sigma 70-200 f2.8 are superb. Pricy glass, though (600 used for the Tamron, 1000 or so for the Sigma). It's also very heavy and long (quite huge, really). Were I you, for mostly indoor sports, I'd pick up a used K-30 and the Tamron 70-200 f2.8 (also used), and maybe an 18-55 for walking around.
For outdoor sports, there's more light, so the Pentax 50-200 is fine, and that's a pretty cheap lens, not huge at all. If it is outdoor mostly, go for the 18-55 and 50-200 setup.
Edit, just saw the budget comment.
At your budget, the 18-55 and 50-200 is your best bet. Indoors, use TAv mode, set ISO to 3200, aperture wide open, shoot in RAW, and use Lightroom (or Topaz denoise) in post to remove the noise.
Also, if it's your first DSLR, don't expect great shots at first, there's a learning curve. Read "understanding exposure", a great book on the exposure triangle.
If you want indoors without a flash, 50mm is too long. Save up, get the Sigma 30/1.4.
Last edited by Kozlok; 03-10-2014 at 08:44 PM.