Vale Tudo, which means "anything goes", is a form of submission fighting which originated in the 1920s. In this form of fighting, virtually nothing was off limits---head butts, groin shots, brutal choking or neck punches, and bare knuckle shots to the face and groin were all par for the course.
Initially fights like these took place in carnivals in Brazil between fighters with different martial arts and wrestling backgrounds until the 1960s when these fights were deemed too brutal--which led to them being banned at public events. At that point Vale Tudo competitions went underground.
In the 1990s, the UFC events inspired a resurgence of interest in a wider variety of combat sports, which brought Vale Tudo back into the mainstream, albeit with more regulations and boundaries.
This video is a good example of the raw, primal quality of Vale Tudo fighting.