I gota agree with Sean. You're likely not going to be very impressed with the results that you'd get from an on-camera flash in an arena - so many factors are working against you. You asked if players might find your on-camera flash distracting - yes, quite likely - you're introducing a very powerful (albeit quick) light from a single point; it's unbalanced within the space. Another problem that I've come across is that unless you're able to provide all the light for the shot from just your flash (i.e. you're not just adding supplemental lighting to the shot), the white balance in your images are likely to look really bad because you'll end up with two different light sources with differing colour temperatures (and to make things worse the colour temperature from arena lighting - metal halide, fluorescent, etc... - actually fluctuate about 60 times a second). Sure you can likely tweak the white balance in post-processing, but that takes time. That's why most professional sport photographers prefer to use enough flash units that all(or at least the vast majority of)the lighting for shots is being supplied by flash units only. Easier said then done - you'd likely be looking at more than 10-16 flash units placed around a hockey arena, but you'd achieve consistent colour, faster shutter speeds and you wouldn't be distracting players with flash coming from one point. A much cheaper option would be a faster lens (e.g. f/2.8, f/2, f/1.8, f/1.4, f/1.2).