For skateboarding, start with roller skating not skiing! If there are rules and an element of competition, both of which should be pretty easy to organise for skateboarding, then it's a sport. If you want to get classical, then it satisfies the first of citius, altitus, fortius. The list of sports that have been introduced to the Olympics then dropped is quite long, I'm not going to speculate if or when skateboarding will join it.