Completely depends what you mean...
What is "chess"? Two kids playing a game inventing rules as they go along(Id say that isnt sport)? Two masters playing for the crown in a heated competition(Id say that is)?
What is "sport"? A purely physical activity where a ball is required(then it wouldn't be but neither would curling, track or weightlifting)? An organized past-time with competition on a larger scale, with physical exhaustion(then it would be)?
In the end though, I honestly don't care.
I have only ever seen my ratings drop