biscuit
Veteran
I believe the International Olympic Committee would beg to differ. The World Chess Federation (FIDE) is one of the largest sports federations in the world, and is officially recognized by the IOC as a sports federation. ( See http://www.olympic.org/chess ) Given this fact, I see no reason to think that cubing is not a sport. The problem with the definition of "sport" that you are using is that it's too narrow. Most words have multiple meanings. By way of analogy, the term "meat" can mean specifically mammal flesh, but in another sense it can also refer to poultry, nuts, fruit, and a variety of other things. (Just trying to get to the meat of the issue.)
The definition I used is the first result that I got. I didn't have to dig for it. I tried to find a definition that doesn't require it to be physically taxing. Let's face it. Cubing does NOT take a ton of energy. It's not physically hard it's not a sport.
And no chess is not a sport. Period.