Christmas over, criticise rising French leader (8)
I believe the answer is:
napoleon
'french leader' is the definition.
(I know this)
'christmas over criticise rising' is the wordplay.
'christmas' becomes 'Noel' (Noel can mean Christmas).
'over' becomes 'o' (cricket abbreviation).
'criticise' becomes 'pan' (informal term meaning to criticise heavily).
'rising' shows that the letters should be reversed in order (in a down clue, letters go up).
'noel'+'o'+'pan'='noelopan'
'noelopan' back-to-front is 'NAPOLEON'.
(Other definitions for napoleon that I've seen before include "Corsican conqueror" , "Corporal and emperor" , "Leading pig in Animal Farm" , "Head pig on Animal Farm" , "no longer tender" .)