Man in charge last to quit ruling (5)
I believe the answer is:
edict
'ruling' is the definition.
(I have seen 'Authoritative ruling ' mean 'edict' so perhaps 'ruling' could also mean 'edict')
'man in charge last to quit' is the wordplay.
'man' becomes 'ed' (short for Edward).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'last to' suggests the final letters.
The last letter of 'quit' is 't'.
'ed'+'ic'+'t'='EDICT'
(Other definitions for edict that I've seen before include "Regulation" , "Order issued by an authority" , "Authoritative decree" , "Formal announcement" , "Formal proclamation" .)