Define "sport" for me

[Wilco23]

My friends and I have this ongoing debate about what qualifies as a "sport." In my definition, it takes 3 things: (1) mental ability / strategy implementation; (2) physical ability / execution; and (3) defense.

The third point is usually the one of contention because it eliminates activities like golf as a sport. While I think golf takes skill and is a competition, I don't think it is a sport. A sport should necessarily allow for your opponent to affect your play in some manner. In golf, it's merely the lowest score wins; it doesn't matter what your opponent shoots if you can't score low yourself, and your opponent cannot alter your stroke or make you shoot worse through some sort of defense.

Thoughts?