If the defendant in a tort action was authorized to do the act complained of, he may plead such authorization as justification. The effect of such plea is to admit that the act was done and to entitle the defendant to all the privileges of one holding the affirmative of the issue. Such plea, however, shall not give the defendant the right to open and conclude the argument before the jury unless it is filed before the plaintiff submits any evidence to the jury.
OCGA § 51-11-1