Clever person hit on head (5)
I believe the answer is:
brain
I believe this clue is a triple definition!
'clever person' is the first definition.
(I've seen this before)
'hit' is the second definition.
(braining is a kind of hitting)
'on' acts as a link.
'head' is the third definition.
(synonyms)
(Other definitions for brain that I've seen before include "Mastermind" , "It controls the central nervous system" , "Clever person" , "The grey matter" , "Organ of the intellect" .)