Originally posted by TaoMaas
I'm gonna guess that the white wall in the background is part of the reason your pics came out dark. That much white in a picture can sometimes fool the light meter. But the good news is that you've already done enough experimentation to know about what settings you'll need for the next event. It's highly unlikely that the lighting inside the arena will change. And you already know that shooting at ASA3200 at 1/200th at f8 gives pics that are too dark. If I were you, I'd start out by changing your f-stop to f5.6 (or whatever the widest is on your 55-300) and leave the ASA and shutter speed alone. Then, if the pics are too bright, I'd bump up the shutter speed until you're getting shots that are exposed right. The faster shutter speed will help increase the sharpness by stopping the action a little better.
I'd also change the metering (if it's full frame metering) to either center or the middle range. This could blow out the white background also, so you might want to play with it a bit to see exactly what works best with the lighting/background of that environment.