I personally don't consider it a sport. However one could argue that parkour is not a sport, because it requires no equipment whatsoever and you're just walking around. Skiing is something you can't just do, you need skis and snow. If I'm walking down a trail and there's a log in my way so I jump over it is it a sport? Now if I jumped over that same log, and decided I'd put some new equipment on my feet that allows me to slide around on the log, then it could be what most people consider a "sport". You can't consider walking around a sport