In dreams, facets of personality that never get displayed in waking life can become quite animated. Nowhere is this more apparent than with violent behavior. The violence may be justified or random, but it is often extremely graphic. It is so graphic, in fact, that you should understand that this is normal-albeit disturbing-and that its presence is almost always an exaggeration of another point.
Violence can be an off-shoot of heroic behavior, especially in rescuing dreams. Terrorism in the news has made all of us aware that the enemies can be in our midst. Kidnapping dreams, escape dreams, and protecting dreams are other versions of this type of violence.
Violence may come unexpectedly, as well (suddenly, you are just stomping some poor guy's head with no apparent provocation).
Often these dreams deal with repressed anger towards authority figures. While wanting to become physically aggressive toward others is a common desire, it should never be acted on in waking life, and it very rarely is. However, the dream releases the anger for you. If you have recurring dreams of this nature, you may want to consider a mediated session with the object of your anger; or re-arrange your circumstances.
If you are the aggressor, does the violence frighten you or make you feel powerful?
If you are the witness to violence, do you feel ambivalent to it or does it somehow affect you?