The defense doesn't have to prove the defendant's innocence. Rather, the burden of proof sits solely with the prosecution. On occasion, the prosecution will mount an extremely weak case. In most instances, however, defense lawyers present some type of case. They will either try to show that the prosecution did not prove beyond a reasonable doubt that the defendant is guilty, or give an affirmative defense.
Affirmative defenses are essentially legal excuses for committing a crime.
For example, the defense may explain that the defendant committed the crime in self-defense or under extreme duress. Or, the lawyer may argue that police entrapped the defendant. The prosecution then has the chance to pose some questions of its own to undercut the witnesses' testimony and make them appear unreliable. Redirect Following cross-examination, the defense can ask the witnesses additional questions in an attempt to undo any damage done by the prosecution. This process is called redirect.