Dionysus: "If the town of Thebes becomes inflamed and tries to oust my Maenads from the mountains, I shall go out there myself and lead my Bacchants in battle." (1)
From the very beginning there is a threat of violence in the play. Dionysus swears not to take any disrespect from Thebes, and he proves himself to be true to his words. This statement from Dionysus is the first hint of all the terror that is to come.
Soldier: "The animal [Dionysus] we found was tame, sir: put himself without resistance in our hands" (31)
Dionysus doesn't put up a fight when he's caught by Pentheus's men. Though he's capable of obliterating them all without any effort, he casually walks into Thebes. We wonder why he bothers with the deception. Could he be luring Pentheus into a sense of complacency? What do you think?
Herdsman: "You could see a woman with a bellowing calf actually in her grip, tearing it apart. […] ribs and cloven hooves being tossed high and low; and blood-smeared members dangling from the pines" (119)
OK, here comes the violence. The Maenads enact their rage at the intrusion of the Herdsman and his buddies by ripping apart the men's cattle. This horrific dismembering could also be seen as a sacrifice to Dionysus.
Herdsman: "The villagers […] took up arms against the manic ones [Maenads] Then what a spectacle, my king, how sinister! Their spear points drew no blood!" (119)
The villagers are completely defenseless in the face of the Maenads. When they try to meet the crazed women's violence with violence, they only bring more destruction on themselves. It seems there is no fighting with the will of the gods.
Dionysus: "you must not take up arms against a god." (122)
No kidding. Dionysus, in the form of the Stranger, warns Pentheus again and again not to try and use violence against Dionysus's followers. It's the same thing as trying to strike at Dionysus himself. The central spine of The Bacchae is a chain of increasingly violent reactions from the god and his followers against Pentheus's blasphemies.
Pentheus: "a most appropriate sacrifice women's blood and massacre in the glens of Cithaeron." (125)
The King seems to be fully prepared to slaughter all of Maenads. Wait, aren't they his own people? Aren't his mother and aunts the leaders? It seems that Pentheus's obsessive refusal to accept the ways of Dionysus has turned him into a real monster.
Dionysus: "Pentheus murdered in his mother's grasp will come to know full well at last Dionysus, son of Zeus, a god indeed" (170)
Dionysus lays his plan for punishment right out there. When Pentheus dies at the hands of his own mother it's no surprise. Of course, Euripides didn't risk ruining the ending for his audience since they all knew the myth anyway. The harsh violence of Pentheus's death is still pretty shocking, though, once the playwright gets done describing the grisly details. In ancient Greek tragedies, it was not what happened that the audiences came to see, but how it happened.
Messenger: "Gripping his left hand and forearm and purchasing her foot against the doomed man's ribs, she dragged his arm off at the shoulder" (225)
Not only is Pentheus killed by his own mother, but he is also literally ripped apart. The horrific violence of this act is a punishment for both of them. It's also a spiritual act. Just as earlier in the play cattle were dismembered in the name of Bacchus, now a human being is sacrificed for the sake of the god.
Agave: "Celebrate my hunting prowess." […] Cadmus: "Murder is what your tragic hands have done. Beautiful the victim cut down by the gods: the sacrificial feast you call me to and Thebes." (263)
Here we have the same violent act of Agave dismembering her son described in three different ways. Agave calls it hunting, while Cadmus relates it to murder and sacrifice. What's the difference between the three acts do you think? How do you separate one from the other?
Cadmus: "he [Cadmus] must lead barbarian mongrel hordes against our Hellas" (319)
Cadmus is doomed to live a life of violence. He must lead foreign soldiers in battles against other Greeks. We wonder why this particular fate was put on the old man. It doesn't quite seem to have the same ironic twist as the rest of the play. Some scholars think that this ending was added in later years after Euripides's death, which would explain its incongruity.