Bodyguard employed by firm in Derby (6)
I believe the answer is:
minder
'bodyguard' is the definition.
(I've seen this before)
'employed by firm in derby' is the wordplay.
'employed by' says the answer is hidden in the clue.
'MINDER' is hidden within 'firm in derby'.
(Other definitions for minder that I've seen before include "One who looks after (someone or something)" , "Bodyguard (colloq.)" , "One who objects" , "One looking after" , "baby sitter?" .)