In Act IV of The Crucible, what had happened in Andover?

When the witch trials began, those first accused were powerless people who occupied the lowest level in their Puritan society. They were not recognized as being worthy or respectable, which contributed strongly in their being singled out for prosecution. As the trials continued, however, the accusations reached higher and higher into Puritan society; suddenly, no one was safe from arrest and punishment. When the nature of those accused began to change, the people became less enthusiastic as general fear and discontent with the proceedings developed.

In the Puritan village of Andover, witch trials were being conducted simultaneously with the trials in Salem. In Act IV, word reaches the court in Salem that the people of Andover have risen up and thrown out the court in their village, putting an end to the prosecution and persecution. This news is especially disturbing to the court in Salem where the hangings continue, now with the most respectable and upstanding people of Salem, such as John Proctor and Rebecca Nurse, scheduled to die. The judges fear the rebellion in Andover will spread to Salem, which makes it imperative to get a confession from one of the respected citizens about to die. A confession from John Proctor, in particular, would serve to legitimize the court's proceedings.