Easiest way to explain lawful assaults is if it is:
Authorised
Justified or
Excused by law
Then it is legal.
I thought practical examples were better to explain than theory, but in hindsight a hybrid of both our answers was probably best.
But,
"Excused by law" makes an act
legal? You sure about that my learned friend? Sorry to get academic here, and you may have a point at a practical level, but my understanding of say assault committed under compulsion, does not make their assault lawful or legal, but merely that the defendant should be
excused from being punished as their will was overbourne. They escape liability as not being blameworthy, but that is not the same as saying their act is lawful or indeed legal. That is my understanding of House of Lords judgments. Has Australian State legislation or HCA declared otherwise, that excused acts are lawful or legal?
Authorised or Justified clearly make an act legal. But excuses just escape criminal liability as I understand it.
Can you answer my other questions about corporal punishment and physically disciplining your kids?