This is kind of a quagmire, if you think about it. Some people are adamant about not shooting at running or moving animals, not shooting too far away from animals when you don't reasonably expect to hit them or anything else that isn't deemed sporting or fair. There's nothing wrong with that but where does that "self imposed rule"apply for wing shooting birds, rabbits on the run, etc.?
Most hunters would say limit yourself to taking shots where you have a reasonably high probability of killing the animal quickly and humanely. For some people, that might mean a running shot at closer ranges. For others, it might mean shots beyond 300 yards (it isn't for most) whereas for some people, shooting beyond 50 yards is dangerous for everybody except the animal. In some ways, I kind of think it depends upon the individual hunter.