Boy, passionate, upset girl (6)
I believe the answer is:
'girl' is the definition.
(I know that damsel is a type of maid)
'boy passionate upset' is the wordplay.
'boy' becomes 'les' (short for Leslie).
'passionate' becomes 'mad'.
'upset' shows that the letters should be reversed in order.
'lesmad' reversed gives 'DAMSEL'.
(Other definitions for damsel that I've seen before include "Maid" , "distressed girl?" , "Girl (literary)" , "Old-fashioned young woman" , "An old girl, often in distress" .)