Ah. No responses to drone. To be expected from the right wingers on here when their narrative is fucked by a logical question!
Who could see that coming...?
Anyway, UK law allows the claim of self-defence "in the defence of another". So you can step in and strike someone to defend your sibling, but the force you use must be "necessary and reasonable" in the circumstances.
The right to use force in the defence of another is established in both Common Law and statute (primarily the Criminal Law Act 1967 and Section 76 of the Criminal Justice and Immigration Act 2008).
It happens in two parts when in a court of law:
The Subjective Test:
Did you genuinely believe force was necessary to protect your sibling from an imminent attack? (Even if your belief turned out to be mistaken, it can still be used as a defence, as long as it was honestly held).
The Objective Test:
Was the level of force you used reasonable and proportionate to the threat?
You're allowed to use the minimum force needed to stop the threat and if the attacker has a weapon, striking them might be reasonable.
"If the person attacking your sibling is a police officer executing their duties unlawfully (e.g., an unprovoked or brutal assault), the same self-defence laws apply. However, if the police officer is carrying out a lawful arrest or action, intervening with physical force to stop them could result in you being charged with a crime such as obstructing or assaulting a police officer in the execution of their duty."
So, if the accused has been found 'not guilty', it will have been contextualised about provocation to trigger the 'self-defence' clause.
Finally, the law makes allowances for the heat of the moment. The courts recognise that when acting instinctively in a moment of unexpected anguish, you cannot be expected to measure your defensive action with perfect precision.
All these factors would have come into play over anyone's perceived ethnicity for the jury under instruction from the judge.