Joseph Maguire gives different views on why violence is in sports:
While legal scholars have sought to distinguish legitimate from illegitimate sports violence, social psychologists and sociologists have investigated the causes of sports-related violence. Here the discussion revolves around broader nature-nurture debates and the role that sports are believed to play in society. Those who believe that aggression and violence are “natural” tend to view them as instinctive and inevitable aspects of human behaviour. From the perspective of Konrad Lorenz and others in this camp, sports are seen as a form of catharsis; they allow for the safe and channeled release of the aggression that is part of every person’s instinctive makeup.
Most sports sociologists, however, challenge this hypothesis and believe instead that research confirms that violence and aggression are socially learned. This latter view is supported by the fact that the levels and types of sports-related violence vary greatly from culture to culture, which strongly suggests that they are not the result of some universal human nature. Canadian ice hockey, for example, is more violent in some respects than its Scandinavian counterpart. The reason for this is that Canadian ice hockey provides a subcultural context in which boys and young men are introduced to highly aggressive behaviour. In this and in many other sports subcultures, brutal body contact and physical assault are part and parcel of what it means to be a man. Conformity to the code of toughness certifies a player’s masculinity and confers upon him honour and prestige. Those who fail to meet such expectations drop out of the subculture or are subject to peer sanctions.
Source: Maguire, J. (2006 December 6). [Weblog] Violence and sports–Ugly but useful? Britannica Blog.