Lens for portrait and other stuff?

I am looking for a lens that I can shoot portraits or Team Photos so it has to be pretty sharp. I would also like to be able to use it for sports close to the action stuff.
My 18-50 (but it's the DC cheaper version) is pretty good, but focus is way to slow for sports, and I want a little bit better image quality....need to fill the gap from my 70-200 and down.

So whats your pick of lenses for this?

You said portrait, but you also want big group photos? I was goign to suggest the 50mm 1.4 or 1.8 for portrait. But now i'm going to. I say trade in your sigma 18-50 DC for the newer Sigma 18-50 EX with constant F2.8 That should fill the void for you and it focuses pretty fast. Not sure if it's fast enough for sports however.