[pstuart]

Can they knock a person down? Then we're talking about the possibility of serious injury or death. It doesn't have to be the initial impact, just what happens after that...

[dzhiurgis]

Can't you knock a person by walking? Or by shouting and spooking them? Or by making a funny face?

Are children allowed to ride bikes on sidewalks in your country/state/city? If so, can't they murder someone with that bike?

[xapata]

Probabilities matter.