Canadian Criminal Law/Defences/Acting in Authority

General Principles

Protection of persons acting under authority
25. (1) Every one who is required or authorized by law to do anything in the administration or enforcement of the law

(a) as a private person,

(b) as a peace officer or public officer,

(c) in aid of a peace officer or public officer, or

(d) by virtue of his office,

is, if he acts on reasonable grounds, justified in doing what he is required or authorized to do and in using as much force as is necessary for that purpose.

– CCC

When considering the use of potential excessive force, the court should consider "the reasonable belief of the officer in all the circumstances as they existed at the time which belief must be justified by the facts at the time." The belief must be subjectively held as well as objectively reasonable.