The Chorus in Sophocles' Oedipus Rex plays a very specific role. It is the voice of the common people, and their view of Oedipus their king changes over the course of the play. The words in your question--"wild, impious, and violent"--are descriptors of King Oedipus.
At the beginning of the play, Oedipus is still seen as their savior. If he saved them once (from the Sphinx), he can surely do so again. The Chorus champions Oedipus in every way. As soon as the blind prophet Teiresias arrives and is abused by Oedipus, though, the Chorus begins a subtle shift in thinking regarding their king. When Oedipus treats Creon with vitriol (hatred) and accuses him of treason, the Chorus no longer defends his actions; and once the entire truth has been revealed, the Chorus feels only pity for their formerly proud king.
That middle position--between adulation and pity--is where they see Oedipus as being "wild, impious, and violent." He has hit an old blind man, made outrageous accusations against his brother-in-law, and called down curses on what turns out to be his own head. They say he is "quick of temper," and they are right. Once the truth is fully revealed, the Chorus sees a patricidal murderer, a usurper to the throne, and worse--one who committed theimpious action of marrying one's own mother. The people, as represented by the Chorus, finally see the truth of Oedipus's character.