Treat in a way that could damage staff name (9)
I believe the answer is:
Here is my best explanation:
'treat in a way that could damage' is the definition.
The answer and definition are not the same part of speech.
'staff name' is the subsidiary indication.
'staff' becomes 'man' (manning is a kind of staffing).
'name' becomes 'handle' (**).
(Other definitions for manhandle that I've seen before include "Mistreat", "treat roughly", "Move by human effort alone", "Push (someone) about roughly", "Knock around", "Roughly treat", "Give rough treatment to", "Treat roughly, or move by human effort alone" and "Rough up".)