Have you ever seen someone fall through the metal coverings on the sidewalk?

I was walking up 9th Ave today and saw a crazy guy jumping on the all the metal coverings that lead to the basements under buildings. He was jumping with such force I was sure one of them was going to give in. Has anyone ever seen one of the coverings give in? Also, doesn't it seem like there are more crazy homeless people invading Hell's Kitchen than usual? I'm used to the regulars around my block, but lately I feel like I'm seeing more and more.