Hit hard — huge anticlimax (6)
I believe the answer is:
bathos
'anticlimax' is the definition.
(synonyms)
'hit hard huge' is the wordplay.
'hit' becomes 'bat' (batting is a kind of hitting).
'hard' becomes 'h' (abbreviation used in pencil classifications).
'huge' becomes 'os' (abbreviation for outsize).
'bat'+'h'+'os'='BATHOS'
(Other definitions for bathos that I've seen before include "Anticlimax by unintentional shift from the sublime to the trivial" , "Ludicrous anticlimax" , "Unintentional slip from serious to trivial mood" , "Anticlimax, descent to something trivial" , "Serious-to-trivial switch" .)