Bully's hard on men receiving shocking treatment (6)
I believe the answer is:
hector
'bully's' is the definition.
(synonyms)
'hard on men receiving shocking treatment' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'men' becomes 'OR' (military abbreviation for other ranks).
'receiving' indicates putting letters inside.
'shocking treatment' becomes 'ect' (electro-convulsive therapy).
'h'+'or'='hor'
'hor' going around 'ect' is 'HECTOR'.
(Other definitions for hector that I've seen before include "Greek fighter" , "Intimidate by bullying, like Trojan prince killed by Achilles" , "Nag" , "Browbeat, bully" , "Boy - bully" .)