Why is John Procter arrested at the end of this act?

John Proctor is arrested at the end of Act III of Arthur Miller's "The Crucible" after he confronts the court and exposes the falsehood of the witch trials. He presents evidence that Abigail Williams and the other girls are lying, but the court dismisses his claims. In a desperate attempt to defend his wife, Elizabeth, Proctor's anger and defiance lead him to admit to adultery, which ultimately backfires and results in his arrest. His actions underscore the hysteria and injustice of the Salem witch trials.