I just did a nighttime event (parade and Christmas event) and used a flash (SB 600) in some and not in others.
I upped the ISO to 640, used a fast lens (f/1.8) and also used shutter speed priority in many shots with people, set to 1/15. This was slow enough to let the right amount of light in but also fast enough to freeze the action and also to stop any camera shake from hand holding the camera. Of course using a tripod would help with that as well, but in my situation , I could not use a tripod.
Of course you will have to experiment with settings yourself, you might have to up the ISO more depending on the ambient lighting. But try out the shutter speed priority. I could not go full manual out there in the dark with all that action and aperture priority, at the widest I could go, still didn't give me enough speed to not have blurry pictures. Shutter speed was the answer.