Though some initial reports claim the root of the incident has more to do with other factors outside their hometown teams, the possibility of a bitter sports rivalry leading to someone's death is a scary thought.
A few months ago, a Bostonian Yankees fan was hospitalized after being jumped by four Red Sox fans, simply because the man was wearing a Yankees cap. There is no winning side regarding behavior as despicable as these two incidents.
If a human-being is so demented in his fanhood for a particular professional sports team that he or she resorts to physical violence, their allegiance has become a mental disorder.
Talking some trash to a rival fan is not uncommon or dangerous, but every mentally stable person understands the broad line between ribbing an opponent and resorting to physical aggression. Such behavior gains nothing but prison sentences, embarrassment and some hospital bills.
Get a life outside of baseball, because when your team wins a championship, they won't be sending you a ring.