This debate occurs on these forums too? Hm, maybe I should read this subtopics more often.
Although I do a lot of chess, I have to say that chess is not a sport. The definition of a sport is "An activity involving physical exertion and skill in which an individual or team competes against another or others." Unfortunately, chess does not directly involve physical exertion (although anyone who plays serious competitive chess will agree that it is very physically demanding). Therefore, chess is not by definition a sport.
However, it is interesting to note that many laws that apply to sports are also applied to chess teams. For example, I was blocked from playing with another school on the grounds that sport teams under the school name must be comprised of members of that school/district. So in a legal context, it appears that chess is being considered a sport.
Many major chess events are similar to big sports events. While obviously they don't have huge turnouts of spectators (though many will be surprised at just how many watch). There are team olympiads, world championships, national championships, and the like. Many events draw thousands of participants. It certainly seems like it may qualify as a sport, even if it does not fit the formal definition. The real underlying motivation behind chess being considered or not considered a sport is the public funds that may be allocated in the case of being classified as a sport.
Among chess players, there is a huge display of sportsmanship, arguably more than professional sport players. Not showing such sportsmanship leads to ridicule and actual action. In this way, chess players consider themselves to be playing a sport.
Basically, chess as a sport follows 3 principles: a) It is not, by rigorous definition, a sport b) It is considered a sport by many, regardless of this definition, and c) it really doesn't matter
