A shadow defense is a legal defense that cannot be sustained on its own merits, but which opens the door to introducing evidence that will assist in seeking jury nullification

Jury nullification

Jury nullification occurs in a trial when a jury reaches a verdict contrary to the judge's instructions as to the law.A jury verdict contrary to the letter of the law pertains only to the particular case before it; however, if a pattern of acquittals develops in response to repeated attempts to...

, and gives the jury

Jury

A jury is a sworn body of people convened to render an impartial verdict officially submitted to them by a court, or to set a penalty or judgment. Modern juries tend to be found in courts to ascertain the guilt, or lack thereof, in a crime. In Anglophone jurisdictions, the verdict may be guilty,...

 an excuse to acquit. An insanity defense might be used to present evidence about a person's troubled childhood, for instance, or a defendant might claim self-defense

Self-defense

Self-defense, self-defence or private defense is a countermeasure that involves defending oneself, one's property or the well-being of another from physical harm. The use of the right of self-defense as a legal justification for the use of force in times of danger is available in many...

 or duress

Duress

In jurisprudence, duress or coercion refers to a situation whereby a person performs an act as a result of violence, threat or other pressure against the person. Black's Law Dictionary defines duress as "any unlawful threat or coercion used... to induce another to act [or not act] in a manner...

 in order to present evidence about an abusive relationship that, nonetheless, did not present an imminent mortal danger to the defendant. An entrapment

Entrapment

In criminal law, entrapment is conduct by a law enforcement agent inducing a person to commit an offense that the person would otherwise have been unlikely to commit. In many jurisdictions, entrapment is a possible defense against criminal liability...

 defense opens the door to presenting evidence about the behavior of police and informants. It is reversible error

Reversible error

In law, a reversible error is an error by the trier of law or the trier of fact or malfeasance by one of the trying attorneys which results in an unfair trial...

 for a trial court to refuse a jury instruction on a theory of defense after a defendant makes a threshold showing as to each element of the defense.