Fellow on ground zero stood still (5)
I believe the answer is:
froze
'stood still' is the definition.
(freezing is a kind of standing still)
'fellow on ground zero' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'on' means one lot of letters goes inside another.
'ground' indicates anagramming the letters ('grind' the letters into a new form).
'zero' with letters rearranged gives 'roze'.
'f' inserted within 'roze' is 'FROZE'.
(Other definitions for froze that I've seen before include "Stopped dead" , "Suddenly stood motionless" , "stopped moving altogether" , "E.g. turned to ice" , "suddenly stopped" .)