Track and field meets are always really confusing. For example, there are rarely any signs that specifically say "do not walk directly on the track during a live race or you might get absolutely creamed by a high jumper."
In all fairness, there usually aren't any "please don't pee in the sink" or "remember to not murder the pole vaulters" reminders either, and people seem to avoid any problems with those situations.
Perhaps this girl (who probably suffered some sort of serious injury after the collision) just forgot that aimlessly wandering around a sporting event is a bad idea or just wanted to become a viral video sensation.
Either way, her pain is hilarious.