Think of the climax of a work as the "Point of no return." Once the climax occurs, the audience knows how the work will end. At first, for the audience, it looks like we're going to get our happy ending; Elizabeth has convinced John to lie and admit that he has been guilty of witchcraft. We know this lie will save his life, even though we know he feels guilty about lying and ruining his name. Eventually, John can't take it- he knows his name is more important than living a lie.
Here we have our climax. Once he rips up his confession, we know how this will end. He's guilty in the eyes of the court, and therefore he will hang.
The climax of a play or another narrative work, such as a short story or a novel, can be defined as (1) the turning point at which the conflict begins to resolve itself for better or worse, or as
(2) the final and most exciting event in a series of events.
The climax of The Crucible occurs, according to the first definition, when the court finds John Proctor guilty after he admits that he had been intimate with Abigail Williams.
According to the second definition, the climax occurs when John Proctor decides it is more important to tell the truth than to save his life with a lie. So he tears up his false confession to witchcraft and gives himself over for hanging.
tearing coffession papers by Procter is the climax in the crucible.