Hurdlers fall down in an empty arena as they race to the finish .
People are running .
Hurdlers fall down in an empty arena as they race to the finish.
People are running.
In the second sentence people running could refer to either the hurdlers as they race to the finish or other people coming to their aid.
In the second sentence people running could refer to either the hurdlers as they race to the finish or other people coming to their aid .