Chess is a game. Sports require a physical aspect and chess is mental. Don't think about it too much people or you will find ways to make EVERYTHING a sport. eg.. ironing, putting on pants, eating chocolate bars, doing drugs... etc. You can always find ways to "beat" your "opponent" at anything.
finally someone who got it right :)
Incedientally, if the criteria are having an active offence and defense and mental fatigue qualifies as being sufficiently strenuous then perhaps arguing on the internet is a sport.