Restless type of fellow one would become (6)
I believe the answer is:
fidget
'restless type' is the definition.
'fellow one would become' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'one' becomes 'I' (Roman numeral).
'would' becomes 'd' (I've seen this in other clues).
'become' becomes 'get' (synonyms).
'f'+'i'+'d'+'get'='FIDGET'
'of' is the link.
(Other definitions for fidget that I've seen before include "Restless person" , "Squirm" , "Make small nervous movements" , "Wriggle" , "person always on the move" .)