A guy on a skateboard does a trick on a ramp while others watch on the other side of the ramp .
It is probably the case that a skateboarder knocks over a woman while doing tricks on a sidewalk .
It is impossible that a skateboarder knocks over a woman while doing tricks on a sidewalk .
It is probably the case that a skateboarder knocks over a woman while doing tricks on a sidewalk .
A skateboarder knocks over a woman while doing tricks on a sidewalk .