Unreliable ruler, scoundrel in charge (7)
I believe the answer is:
erratic
'unreliable' is the definition.
('erratic' can be similar in meaning to 'unreliable')
'ruler scoundrel in charge' is the wordplay.
'ruler' becomes 'er' (abbreviation for Elizabeth Regina).
'scoundrel' becomes 'rat' (I've seen this in other clues).
'in charge' becomes 'ic'.
'er'+'rat'+'ic'='ERRATIC'
(Other definitions for erratic that I've seen before include "Irregular and unreliable" , "Irregular, not dependable" , "Eccentric, aberrant" , "Irregular - eccentric" , "Not regular in pattern" .)