WHO, WHAT, WHY?
The Magazine answers...
Assault is against the law but what if it is committed to protect someone else?
Call the police or intervene?
Protecting the vulnerable is considered a key tenet of a civilised society, but recent events have shown that intervention in an effort to uphold community values can come at a very high price.
As well as the recent high-profile cases of men being killed after stepping in to stop troublemakers, there is also the memory of Philip Lawrence, the headmaster who was fatally stabbed in 1995 when trying to save a pupil from a gang.
The dilemma of intervention is one many of us - including broadcaster Jeremy Vine - have grappled with in our minds, if not in reality. But what protection does the law afford the person who commits violence when protecting someone else?
In England and Wales, an assault is usually deemed unlawful unless in self-defence.
Assault is lawful if preventing a crime or protecting family, property or another person
But force must be reasonable and proportionate
"There's the concept of self-defence in case law that extends to defending not just one's self and one's property but also one's nearest and dearest and family," says solicitor Robert Brown.
"If I was married and my wife was being attacked then it would be a form of self-defence by analogy to protect property or family. So to that extent there would be some permission."
This self-defence protection extends to anyone else, including a stranger.
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The Criminal Law Act could also be used. This aims at preventing a crime and permits assault if, for example, a shoplifter is being stopped from leaving a store.
"Therefore by analogy if you see someone beating up a stranger and intervene and you are accused of assault then you could use the Criminal Law Act to say 'I've a defence because I've prevented a crime,'" says Mr Brown.
"Therefore there's a rather broad defence in law to protect someone who intervenes."
The force used must be "reasonable and proportionate" and that is decided by a jury, which should take into account the difficulty of assessing what this means in the heat of the moment.
In Scotland, the self-defence law also applies and it covers actions on behalf of anyone else, says Alasdair Thomson of the Glasgow Law Practice.
Lawrence died helping others
"You can act in self-defence of another in Scots law and you can come to the assistance of a person under threat of imminent physical violence," he says.
"But the response has to be proportionate to the violence that's potentially being meted out. It's not classed as an assault because there's no intent to injure."
And any means of escape has to be taken at the earliest opportunity, for the defence to hold.
But the advice from police is unequivocally against intervention. A spokeswoman for the Association of Chief Police Officers says they have only one instruction - call the police.
And a Home Office statement said: "The public should not intervene in any situations of any criminal activity. They may put themselves in danger, exacerbate the situation and ultimately be acting on the wrong side of the law."
Those who have stepped in have sometimes found the authorities interpret events in an unsympathetic way.
A rail guard who intervened to protect passengers from a man who had allegedly threatened them has reportedly been sacked and charged with threatening behaviour, after appearing to head-butt the man.
And in a separate incident, Magazine reader John, from London, says he was charged with grievous bodily harm after a teenager who had been abusing a woman in a petrol station then squared up to him and threatened to knock him out. John punched the youth and fractured his jaw.
He says he was charged with GBH, suspended from work, depicted as a thug by lawyers and faced the prospect of jail, but the charge was dropped when CCTV evidence clearly showed the youth, who was eventually convicted of affray, behaving threateningly.
"Much as I would want to help out another person who was being attacked or abused, these situations can quickly escalate into violence," says John.
"And even if you don't get hurt as a result, the police are going to get involved, as are lawyers who are smart enough to make the whole thing a lottery."