Fine performance in division (7)
I believe the answer is:
faction
'division' is the definition.
(thesaurus)
'fine performance' is the wordplay.
'fine' becomes 'f' (abbreviation in pencil classifications).
'performance' becomes 'action' (I've seen this in another clue).
'f'+'action'='FACTION'
'in' acts as a link.
(Other definitions for faction that I've seen before include "Cabal" , "Minority who dissents from main group" , "Small trouble-making group within a group" , "part of party" , "Act on if for a small group within a larger one" .)