I do alot of "sports" work, sometimes daylight (which is bonus and delux) and other times at football venues at nite. The latter is most challenging equipment-wise by far. All that said, a flash is not in my kit and I don't believe I'll *ever* use flash on my shoots. Even indoors (gyms, basketball venues) I wouldn't even think of it. Most indoor venues frown upon, or even ban, flash. Outside, distance and the ability to move quickly, not to mention the distraction to performers/athletes, make flash of any kind not advisable. A mantra amongst sports shooters is to get as much shutter as you possibly can. At a dimly lit high school football stadium, for example, I might shoot 24,000 ISO in order to get 1/1000th at f4 (utilizing a Nikon D5 with the 200-400 f4). YMMV in the activity you shoot, and of course venues, but bottom line, for me at least, shutter rules.
