Burdened, with leader gone: it's rotten (6)
I believe the answer is:
addled
'it's rotten' is the definition.
(I've seen this in another clue)
'burdened with leader gone' is the wordplay.
'burdened with' becomes 'saddled' (I've seen this before).
'leader gone' means to remove the first letter.
'saddled' with its first letter taken away is 'ADDLED'.
(Other definitions for addled that I've seen before include "Confused (wits); made rotten" , "Befuddled" , "mixed-up" , "Gone bad (of eggs)" , "became rotten" .)