A sport - I would have thought, was a competition involving human endeavour, humans displaying skill and mastery of what they do, that sets them aside from other humans, either individually - or collectively. Coupled with a measurable metric of achievement to determine a winner and not a basis in artistic interpretation.
The fact that some sports involve greater strength, or ingenuity (skill) is immaterial, surely? Its humans pitted against each other in a defineable competition where one or one set of humans is judged to be better than others.
I would say that a cooking competition isn't - despite fulfilling most of the criteria, but darts is a sporting competition, as it involves human skills, both physical and mental, despite the absence of great physical prowess.
Anything involving the manipulation of a mechanical vehicle, whilst involving human intervention and skill, is far too reliant on the machine, and often a raft of backroom people. Some team stuff there, but no boundaries - the backup team can be as big as you can afford, so the team bit dies (for me.)
Dressage? A sport for me. The horse won't do it on its own.
Golf is a sport, if it isn't, then neither is cricket or baseball. Human skill, mental, physical and teamwork. The macaronic assumption that it ceases to be a skill because a 50 year old can beat a 20 year old is mind boggling. Bobby Charlton at 35 was a far better footballer than just about any 18 year old at the time, did that devalue football as a sport?
From a personal perspective (sorry to bore some of you) I think that competition skydiving should be an olympic sport. Apart from needing an airlift, the sport is entirely down to human skill and endeavour, its not age or sex dependant, although it is often split into gender at competitive level and is all about physical and mental endeavour, with measurable attainment levels that don't require subjective judgements. (although some disciplines do in some competitions)
Just my take on things.