It is unethical to eat game meat that has not been hunted legally. Also, unless it is killed properly (halal), I doubt that it would be okay for a Muslim to eat.
It is faster and less painful than clubbing it multiple times to make it unconscious. Then there are people who can't shoot accurately enough and wound the animal first before finally killing it. If an animal must be killed it should be quick and as painless as possible.
killing just for sport is utterly stupid. They should try golf or something, for f***ks sake. Regulated hunting to keep the population reasonable, and using the meat and the other body parts is much more ethical.