Employer restricted by house rules (4)
I believe the answer is:
user
'employer' is the definition.
(someone who employs or uses something)
'restricted by house rules' is the wordplay.
'restricted by' says the answer is hidden in the clue.
'USER' can be found hidden inside 'house rules'.
(Other definitions for user that I've seen before include "One who employs" , "One who exploits others" , "Drug addict (colloq.)" , "Ruse for employer" , "One who exploits, to be sure" .)