Hard to penetrate top man, unusually shady figure (7)
I believe the answer is:
phantom
'shady figure' is the definition.
(shade can mean a ghost)
'hard to penetrate top man unusually' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to penetrate' is an insertion indicator.
'unusually' indicates an anagram.
'top'+'man'='topman'
'topman' anagrammed gives 'pantom'.
'h' placed into 'pantom' is 'PHANTOM'.
(Other definitions for phantom that I've seen before include "Ghost of the Opera" , "Sightseeing journey" , "Something creepy" , "shadow of his former self?" , "Apparition, spectre" .)