Duty put Harry in mood (7)
I believe the answer is:
tonnage
'duty' is the definition.
(I know that tonnage is a type of duty)
'harry in mood' is the wordplay.
'harry' becomes 'nag' (both can mean to consistently bother).
'in' indicates putting letters inside.
'mood' becomes 'tone' (tone is a kind of mood).
'nag' placed within 'tone' is 'TONNAGE'.
'put' acts as a link.
(Other definitions for tonnage that I've seen before include "Weight of cargo - ship's carrying capacity" , "Charge for carrying" , "Capacity of ship" , "Ship's size or carrying capacity" , "No agent (anag)" .)