[QUOTE=Magrus]See, this, is where I see a problem. If everyone witnessing it has the same view as you, then no one does anything, correct?[/QUOTE]
Actually, I agree with this one. And I think most of the people witnessing thinks that this fight isn't actually their problem, so they don't do anything. I must confess that I think same way. First reason why I won't do anything is, the reason stated here already, that I don't know why the fight begun, and who is actually guilty. The person who is beaten may actually be the attacker.
Secondly, I don't want to get myself hurt. As a basketball referee I have experienced several times situation where player starts beating other player. As a referee I have to do something, usually this means dragging the attacker away. Almost every time I have got several small or a bit bigger injures and wounds. This is because when I try to drag beater away, (s)he is so angry and full of adrenaline that (s)he starts beating me when I not able to beat the other player.
On the other hand, if the situation is not yet bad, I usually try to talk. This mostly doesn't work because, also as stated here earlier, person full of adrenaline doesn't want to listen common sense. Also I try to avoid situations where the attacker is bigger than me, because I have learned that it's not fun to be the target of the angry of guy who is 200cm long and weight is over 100kg (I'm a bit over 180 cm and 60 kg

).
SO, as a conclusion, I believe that if I'm in town and see a situation where someone is beating other, I wouldn't do anything, not even call the police. This is because if I call, I usually have to stay there to wait police, and if the beater notice this, I'm in trouble. So I just walk away, like I think quite many do.