I spent some time trippin out on the age old debate of, "is skateboarding a sport, an art, a lifestyle, is it pointless?" While, yes, it can be all of those things, I think that skateboarding most closely resembles the practice of martial arts.
It is a practice of extreme physical and mental discipline that is completely reliant on the self. It is a journey that is spiritual in nature; you learn life long lessons of failure, discipline, success, respect, and growth. The movements in skating are closer to movements you'd make in something like tae kwan do, not a traditional sport, and you use a piece of equipment (like a weapon) as part of the practice.
At the end of the day skateboarding is anything and everything you want it to be, but in my mind, skaters are related to martial artists more so than a traditional athlete that runs or swims.