What is the threshold for reasonable force when one is being mugged or assaulted?

Question

Bob was mugged and assaulted by a gang of three youths, and when later standing on the side of the street chatting with a stranger about the incident they said that what they would have done if faced with three assailants alone was knock one of the three out with overwhelming force to begin with so there would only remain two standing who would more than likely be scared off anyway.

If Bob followed this perhaps realistically street wise stranger’s advice next time he found himself in such a situation, then legally speaking, would he commit an offence?

Does defensive force have to be of a passive, deflective or evasive nature to be lawful? Or could hitting someone with the objective of subduing them, knocking them down, incapacitating them, or of intimidating or daunting/deterring their accomplices still receive an excuse from the law given the contextual circumstances?

Simply put, what is the threshold of permissible reasonable defensive force when faced with an assault?

Answer 1

england-and-wales

Self-defence isn't available as a defence to charges of sexual offences.

Other than that, there isn't such a "threshold" defined by law. There's no requirement for "passive, deflective or evasive" force.

Consider that self-defence is available as a 'complete defence' to murder, let alone making a person unconscious or breaking their nose or limbs.

All answers to questions of the form "can I use [this force] in self-defence" are essentially the same and well-established.

… It is both good law and good sense that a man who is attacked may defend himself. It is both good law and good sense that he may do, but may only do, what is reasonably necessary. But everything will depend upon the particular facts and circumstances. …

— Palmer v R 1971 AC 814

A person can use force in self-defence. If it comes to legal proceedings, prosecutors will ask if there was any need for any force at all (was it necessary) and was the force used reasonable in the circumstances. Ultimately, in court, the finder-of-fact must ask themselves whether, on the basis of the facts as the accused honestly believed them to be, a reasonable person would regard the force used as reasonable or excessive. In other words the jury or judge must decide whether it was 'reasonable force'.

The defender has no duty to give a warning, to retreat (R v Bird 81 Cr App R 110), or be hit first before he uses force (R v Deana 2 Cr App R 75; R v Beckford 1 AC 130).

The defender has no duty to use a specific kind of force, a specific level of force, or to inflict a specific injury:

… If there has been an attack so that self defence is reasonably necessary, it will be recognised that a person defending himself cannot weigh to a nicety the exact measure of his defensive action. If the jury thought that that in a moment of unexpected anguish a person attacked had only done what he honestly and instinctively thought necessary, that would be the most potent evidence that only reasonable defensive action had been taken …

— Palmer v R 1971 AC 814

The defender increases his risk of being found to use unnecessary or unreasonable/excessive force if he continues to attack the attacker after they have surrendered, are incapacitated or running away. It may be reasonable force if Bob knocked out one of his attackers, causing the other two to run away, but Bob is no longer acting in self-defence if he continues to kick the unconscious attacker.

… If the attack is all over and no sort of peril remains then the employment of force may be by way of revenge or punishment or by way of paying off an old score or may be pure aggression. There may no longer be any link with a necessity of defence. …

— Palmer v R 1971 AC 814

References:

Crown Prosecution Service Legal Guidance on Self-Defence and the Prevention of Crime

Wikipedia Self-defence in English law

Answer 2

canada

In summary:

• The source of Bob's idea does not matter.
• The act needs to be taken with the purpose of defending oneself.
• There is no "threshold" — reasonableness is judged based on all the circumstances.

The reasonableness of the source has no bearing on whether an act is self-defence

You ask (Question 1):

What is the threshold for reasonable source when one is being mugged or assaulted?

and then describe in much detail how Bob got the idea for a potential response in the future.

It doesn't matter that Bob got the idea for potential future actions from a "tough friendly worker" or a "street wise stranger." The source has no effect on a self-defence analysis.

You are describing potential self-defence

You ask (Question 2):

If Bob followed this perhaps realistically street wise stranger’s advice next time he found himself in such a situation, would he commit an offence?

The person claiming self-defence must believe in their mind that "a threat of force is being made against them or another person." That belief must also be based on reasonable grounds. They must also act with the subjective purpose of protecting themselves or the other person from that use or threat of force. And the act must be reasonable in the circumstances.

This all comes from s. 34 of the Criminal Code. It reads:

34 (1) A person is not guilty of an offence if

(a) they believe on reasonable grounds that force is being used against them or another person or that a threat of force is being made against them or another person;

(b) the act that constitutes the offence is committed for the purpose of defending or protecting themselves or the other person from that use or threat of force; and

(c) the act committed is reasonable in the circumstances.

You ask (Question 3):

Does defensive force have to be of a passive, deflective or evasive nature to be lawful?

The act does not need to be "defensive" per se. But the act needs to be taken with the purpose of defending.

Whether the act is reasonable depends on many factors, including the nature and proportionality of the response — there is no "threshold"

You ask (Questions 4 & 5):

Or could hitting someone with the objective of subduing them, knocking them down, incapacitating them, or of intimidating or daunting/deterring their accomplices still receive an excuse from the law given the contextual circumstances? Simply put, what is the threshold of permissible reasonable defensive force when faced with an assault?

Section 34(2) says:

(2) In determining whether the act committed is reasonable in the circumstances, the court shall consider the relevant circumstances of the person, the other parties and the act, including, but not limited to, the following factors:

(a) the nature of the force or threat;

(b) the extent to which the use of force was imminent and whether there were other means available to respond to the potential use of force;

(c) the person’s role in the incident;

(d) whether any party to the incident used or threatened to use a weapon;

(e) the size, age, gender and physical capabilities of the parties to the incident;

(f) the nature, duration and history of any relationship between the parties to the incident, including any prior use or threat of force and the nature of that force or threat;

(f.1) any history of interaction or communication between the parties to the incident;

(g) the nature and proportionality of the person’s response to the use or threat of force; and

(h) whether the act committed was in response to a use or threat of force that the person knew was lawful.

Regarding the proportionality of the response, "a person defending himself against an attack, reasonably apprehended, cannot be expected to weigh to a nicety, the exact measure of necessary defensive action" (R. v. Khill, 2021 SCC 37).

All circumstances are relevant, including the other parties. There is no threshold. Ultimately, whether the act is reasonable is a question of fact left to the jury (or judge as trier-of-fact).