Following up on Linwood's post, here is one of your images tweaked a bit. I bumped up the exposure about a stop. The lightened image looks cleaner, has more contrast, and looks sharper. Perhaps this is all you need to do. That said…
I cannot judge focus, the posted images are too low res. Bur for starters, I'd keep it simple: single, center point AF-C. Once you get results with which you are happy, you can switch to more complex settings such as nine-point.
Overall, it seems that the arena light is your biggest problem — it's not very bright. You are already at ISO 6400 with a wide open aperture, so there's not much more you can do. If, as you view the high res files, the images seem blurred, then you need a faster shutter speed. So put the ISO at 12800 for a few shots and see if that helps.
Given that ISO and aperture are pretty well maxed out and your shutter speed may already be borderline low, I recommend not adding +EV. That will lower your shutter speed and risk blur. Instead, “steal” the extra stop in post processing, as I did on this image:
Jon Kandel A New York City Nikonian and Team Member Please visit my website and critique the images!