What makes a group of men attack a person in such a vicious bloke ner?

when they are waiting for a bus to go home after a night out?http://www.thisisnottingham.co.uk/displaynode.jsp?nodeid=133942&command=displaycontent&sourcenode=229136&home=yes&more_nodeid1=133951&contentpk=18236955#viewsthis has got to be about the worst case of violence this year that has happend to a woman.tbh this has all the hall marks of a video game.i saw the picture of her on the front page and her face is a mess.for someone who has seen some nasty things, it made my stomach turn and my blood boil with rage.shutyerfaceup, i live in what i call "ground zero" where most of the shootings & stabbings have happend and even my postman was stabbed on my doorstep, i was reminded e day until the blood wash off my doorstap, it was the first time i have ever had to use my first aid for such a thing.i have had 3 mugging attempts myself and have various scars to show for it.
Answer
Booze turns men into pack animals