We first see Hale’s faltering belief in the witch trials after John Proctor admits to lechery with Abigail Williams. After Elizabeth tells the court that her husband never committed adultery, destroying John’s chance to end the whole witch hunt by condemning Abigail, Hale shouts to Judge Danforth, “It is a natural lie to tell; I beg you, stop now before another is condemned! l may shut my conscience to it no more - private vengeance is working through this testimony! From the beginning this man has struck me true. By my oath to Heaven, I believe him now.” Although he has made dreadful mistakes, he is willing to admit it, risking his own reputation (which was everything in the Puritan community) to stop any further executions.
When the girls pretend to see Mary as a bird overhead (as a smokescreen to prevent being defamed, of course), Hale looks directly at Judge Danforth and says, “You cannot believe them!...I See nothing, Your Honor!” In this scene, the ludicrous nature of the girls’ accusation becomes ironically apparent to Hale. But the Puritan court has tied its own hands by claiming that God is speaking through the children, and the court does God’s bidding. Even if Hale could make these judges see reality (and it’s entirely possible that they do), they will never go back on their own authority.
So Hale has no choice but to renounce his association with the court. He does as much damage control as he can by first asking Danforth to pardon the accused. When that fails he convinces Elizabeth to ask John to save his own life by signing the confession. He is present until John’s hanging, pleading with her to change her husband’s mind right up to the end.