Why is Reverend Hale considered a dynamic character?

In literature a dynamic character is one who experiences profound change. In the case of the Reverend Hale we see someone radically different at the end of the play from what he was at the start. It is this dynamism that makes him arguably the most complex and interesting character in The Crucible.
At the beginning of the play Hale is a single-minded, fanatical hunter of witches. It is his passionate conviction that Salem is a veritable den of iniquity, infested by those who practice the foulest of black arts. Ominously, Hale sets a great deal of store by outward appearances:
"The devil is precise-the marks of his presence are as definite asstone."
And he is determined to prosecute anyone who shows (in his mind at least) the slightest visible sign of conforming to his notion of what a witch looks like.
Yet Hale's outward confidence in the moral rectitude of his mission is shattered as the play progresses. For one thing, his overriding belief that there are witches round every corner leads to his being duped by the slanderous machinations of Abigail Williams. Ironically, it was Abigail who encouraged Tituba to cast a spell on Elizabeth Proctor. If anything, she is more of a witch than anybody in Salem. And with her lies and false accusations she casts a spell over Hale, though one that is eventually broken.
Although Hale is a changed man by the end of the play he's also a broken man. In a last desperate attempt to bring justice to the accused he pleads with them to confess in order to avoid execution. But by fighting lies with more lies he is simply contributing further to the toxic climate of untruth that has gripped the town. Ultimately, Hale is trapped. He wants to do the right thing, to bring justice; but he cannot truly do so without challenging the very foundations of the practice of witch-hunting to which he's devoted so much time and energy.