Marbles man — Nigel, possibly (5)
I believe the answer is:
elgin
'marbles man' is the definition.
(I've seen this before)
'nigel possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'nigel' with letters rearranged gives 'ELGIN'.
(Other definitions for elgin that I've seen before include "He removed marble sculptures from the Parthenon" , "here in Britain?" , "The -- Marbles (British Museum)" , "Marbles man" , "English lord" .)