The commonsense view is that it is good, especially for boys and adolescent males, to participate in violent sports such as football, boxing, rugby, North American hockey, and mixed martial arts. The reason is that it gives them a way to release or vent their pent up aggression through acts of controlled violence in organized sport. The idea is that it is better that they do it in such relatively harmless ways.
But, in their new book, philosophers of sport Mark Holowchak and Heather Reid point out that while "the data are not unambiguous, current research indicates strongly that exposure to aggression leads not to catharsis, but rather to heightened aggression" (p. 87). According to the authors, this poses a major obstacle to reforming contemporary sports, which are largely driven by martial abilities and market forces. Rather than sublimating violent behavior, the evidence, when examined carefully, shows that exposure to aggressive behavior leads to heightened aggression or more frequent aggression. This means we should reconsider our devotion to the sports mentioned above, because by "...condoning aggression in sport, we contribute to aggression and violence in society" (p. 92).