A redirect examination takes place during a trial after the cross examination of a witness has been completed. During a redirect, the lawyer who called the witness has an opportunity to clarify the testimony of the witness, in an attempt to minimize potential damage and explain the testimony. The right to a redirect is not always taken by a lawyer, although unexpected or potentially dangerous testimony will often evoke a redirect. After the witness goes through this process, he or she is thanked and dismissed.
The process of calling a witness tends to be rather complex. Usually, lawyers meet with the witnesses they call before the trial starts, to cover the questions that the witness will likely be asked, along with his or her responses to those questions. While explicit coaching and an incitement to commit perjury are not legal, a lawyer can certainly review testimony with a witness to make it stronger. As a general rule, once a witness in on the stand, the lawyer who called that witness will not ask a question that he or she does not know the answer to. The idea is to present the evidence of the witness to the jury in a convincing way, not to collect new information.
After a lawyer examines his or her own witness, the witness is turned over to the opposition for cross-examination. During cross examination, the lawyer will ask a series of questions which are designed to elicit more information from the witness. Although common in courtroom dramas, unexpected revelations during cross examination are actually quite rare. Usually, the opposing lawyer simply tries to undermine the credibility of the witness.
Once cross examination is complete, the judge offers an opportunity to redirect to the original lawyer. Typically, the lawyer may only ask questions about material which came up in the cross examination during the redirect. This is because the opposing lawyer will not have an opportunity to deal with new or unexpected information from that witness.
Especially in a case where the opposition has tried to undermine credibility, the redirection is an important chance for the lawyer to re-establish key facts and information. For example, if the opposition assaults the eyesight of the witness, the lawyer may clarify the issue in the redirect, indicating that the witness could see the events perfectly well. Or, in a case where professional qualifications are called into doubt, the lawyer may make it clear that the witness is an expert in his or her field.