What is the test for giving an instruction regarding any legitimate defense that is supported by the evidence?

The district court must give an instruction regarding any legitimate theory of defense that is supported by the evidence, and a failure to do so is reversible error. United States v. Polizzi, 801 F.2d 1543, 1549 (9th Cir.1986). Further, a defendant is entitled to an instruction concerning his theory of the case if the theory is legally sound and evidence in the case makes it applicable, even if the evidence is weak, insufficient, inconsistent, or of doubtful credibility. United States v. Doubleday, 804 F.2d 1091, 1095 (9th Cir.1986), cert. denied, --- U.S. ----, 107 S.Ct. 1628, 95 L.Ed.2d 201 (1987).