In a typical criminal case, the Crown Prosecutor leads evidence in an attempt to prove beyond a reasonable doubt all the essential elements of each of the charges before the Court. When the Crown has concluded its case, the Court invites the accused to call evidence. Before deciding whether to call evidence it is open to the accused to bring an application for a directed verdict of acquittal on the basis that no reasonable jury, properly instructed, could return a verdict of guilty.

A directed verdict of acquittal (also called a non-suit) is a creature of the common law.

R. v. Litchfield, 1993 CanLII 44 (SCC).  

A directed verdict takes its name from the fact, that historically, the trial judge literally directed the jury to return a verdict of not guilty (a procedure which was reformed in 1994 in R. v. Rowbotham, [1994] 2 S.C.R. 463).

It is only after the prosecution has formally closed its case that an application for a directed verdict can be brought.

The test a trial judge is to apply on an application for a directed verdict is the same as that which an extradition judge or a judge at a preliminary inquiry must employ: is there is any evidence upon which a reasonable jury properly instructed could conclude that the accused is guilty beyond a reasonable doubt? [FN1]

See for instance R. v. Arcuri, 2001 SCC 54 (CanLII), at para. 21;

United States of America v. Shephard, 1976 CanLII 8 (SCC).

Ergo, a directed verdict will be granted if the Crown fails to call some evidence, direct or circumstantial, on each element of the offence. 
Dealing with Circumstantial Evidence

Where the Crown adduces circumstantial evidence, the court must consider whether the evidence considered as a whole (including any defence evidence) is capable of reasonably supporting the inferences sought by the Crown.

It is well established law that on an application for a directed verdict, the trial judge cannot make assessments of credibility and must accept the Crown’s case at its highest.

In some circumstantial evidence cases, there may exist not one, but a whole range of reasonable inferences which may be drawn. Where more than one inference can be drawn from the evidence, the court is not to weigh competing inferences, and only the inferences that favour the Crown are to be considered on the application.
Procedure in Jury Trials    

In accordance with R. v. Rowbotham, [1994] 2 S.C.R. 463, which modified the common law procedure on directed verdicts, the trial judge should enter a verdict of acquittal instead of directing the jury to acquit the accused on that count. [FN2]

As a result of this reform, the application is now also referred to as an application for non-suit.
[FN1] The test for directed verdict employs the concept of a prima facie case, that is, a case containing evidence and all the essential elements of a charge which, if believed by the trier of fact and unanswered, would warrant a conviction.

[FN2] R. v. Rowbotham, [1994] 2 S.C.R. 463: “the trial judge should now say ‘as a matter of law, I am withdrawing the case from you and I am entering the verdict I would otherwise direct you to give as a matter of law.”