Most cultures have had some sort of sports or games. I can think of examples of violent, combat-based, or simply dangerous sports springing up in many times and places: Anetsa (sp?) in eastern American Indian groups, Sumo in Japan, Roman chariot races, American Football, etc. Many people have aggressive urges, and it seems there is often a need in society for some acceptable entertainment that caters to this urge. Sometimes it is in sports, other times it may be through arts (movies) or other outlets. If there is no such violent entertainment in a science fiction world, you will need to have some explanation as to how aggression is handled in this world, and this is likely to be important enough to be a major plot point.