It's been my experience that the best way to deal with up to 4 or 5 agressors goes like this- give the smallest one a coin for the 'phone box, tell him to dial 9 11(999 in england) and ask for an ambulance, just as he asks why, kick the one "with the mouth" straight in the nuts (******** in england) this usulally makes them all start running before he hits the ground! If not I don't tend to worry as I am a karate student. I realise this will not suit everybody, but it has served me very well for many years.
