Seems to me a "sport" should have some quantitative properties (i.e. something measurable, for those of you in the South ;) ). Lines that need to be crossed, balls that must go through hoops, pucks that need to get past a goalie, etc. Sports measure speed (track, MX/SX, drag racing), distance (field events, endurance races), accuracy (shooting sports, archery): most all stick-and-ball sports include all these aspects, as do motorcycle racing.
Don't get me wrong, judged events take a lot of skill to master, but they rely on qualitative properties (how something looks). I'm not sure what to call them, but they ain't sports.
I'm not bagging on any of these events. I find this a very interesting topic for debate.