I think too many types of competitions have been labeled "sports". It doesn't mean those competitions don't require some kind of skill, mental prowess or endurance, but those attributes do not make something a sport. Many of these are better labeled "athletic contests" or something similar. In my opinion, to be a sport, the contest must pass all 3 of these tests:
It must require athleticism more than basic hand/eye co-ordination or endurance - This eliminates those types of contests like poker, darts, competitive eating or other events that you can do while drinking beer at the same time.
Scoring must be done by accomplishment of something as opposed to being judged - Contests like gymnastics or ice skating fall short for me because a 3rd party determines whether you win or not. It also forces boxing, MMA & wresting matches to be decided by one person quitting or being knocked unconscious as opposed to 3 corrupt judges deciding who looked better.
There must be the opportunity to play defense - This brings in the will to win, which in sport can be illustrated by stopping a talented opponent from achieving a predetermined goal. This condition makes a 100 meter dash an athletic contest, while a longer mile run, where you can literally block or hem in an opponent, a sport.
I know these conditions are insulting to some, but that is what I use to draw the line. Ironically, the 3 things I enjoy the most (bass fishing, bowling & poker), I don't consider to be sports, even though all 3 can attract very competitive and skilled contestants.