When can physical force be used outside of personal self defense? If you see someone repeatedly kicking your car can you chase him away? Say someone is at your door step and pushes past you inside, can you use force on them? What if you're carrying your laptop and some nut keeps following you and kicking it?
On another note, if you see someone getting attack, is it legal to intervene by using force e.g. tackling or hitting the attacker?
I am not a Canadian lawyer, but here is the text of the Canada Criminal Code (R.S., c. C-34, s. 27) that appears to deal with justifiable force:
Use of force to prevent commission of offence
27 Every one is justified in using as much force as is reasonably necessary
(a) to prevent the commission of an offence
(i) for which, if it were committed, the person who committed it might be arrested without warrant, and
(ii) that would be likely to cause immediate and serious injury to the person or property of anyone; or
(b) to prevent anything being done that, on reasonable grounds, he believes would, if it were done, be an offence mentioned in paragraph (a).
So, for your hypotheticals: under the letter of the law, you would be able to use force to stop someone from kicking your car or your laptop, so long as the kicking was forceful enough to "cause immediate and serious injury" to said car or laptop. You would also be justified in using force to stop one person from attacking another on the street.
You might not, however, be justified in using force to remove someone from your property unless you had a reasonable belief that the person was going to start smashing up your living room. If they came in and plopped themselves down on your couch and refused to move, I don't believe that you would be justified in using force to remove them.
The big wrinkle is, of course, that you are only allowed under the law to use "as much force is reasonably necessary" to stop something that might be thought, on "reasonable grounds", to incur a "serious injury". (If the guy kicks a few dents in your car, does that constitute a "serious injury"?) Lawyers get paid the big bucks to argue about whether each one of those phrases in quotes was in play in any particular situation.
My interpretation of the law in most western countries you are permitted to defend yourself - but the line between defense and attack is open to interpretation when anger or patience is short. Things get tougher if there are fewer witnesses on what or who started the violence.
Thus if a boyfriend is beating up his girlfriend, I do not believe you have a right to hit the boyfriend, but you do have a right to hold him and prevent him from hitting the girlfriend. If he was to attack you, I suspect you would be within your right to do what you need to do to defend yourself (which could mean knocking him out - but to continue kicking him when he is unconscious or no longer a threat would be breaking the law).
But if in doubt, call the law before things get physical.
