In many respects, John Proctor in The Crucible answers to the traditional definition of a tragic hero. First of all, John's downfall evokes pity and fear in the audience. We feel that John, for all his faults, is basically a good man, and so we feel pity towards him as he endures the ordeal of being falsely accused of witchcraft. John is completely innocent, and there's nothing like the sufferings of an innocent man or woman to evoke pity. We also feel fear, as we know what terrible fate awaits John in the event of his being found guilty of such a serious crime.
Like any classical tragic hero, John also has a tragic flaw in that he's determined to defend his family's good name at all costs. It's this flaw that holds him back from going to the court at the earliest opportunity and telling the judges what Abigail Williams told him: that what the girls got up to that night in the forest was only sport and that Betty's illness had nothing whatsoever to do with witchcraft.
John's pride at his family name prevents him from doing the right thing on this occasion; he doesn't want the Proctor name to be sullied by association with Abigail. Yet, ironically, the Proctor name will, in due course, come to be associated with her in any case, after John dumps her and she starts flinging false accusations at John and his wife Elizabeth.