Boy nuts about girl (6)
I believe the answer is:
damsel
'girl' is the definition.
(damsel is a kind of girl)
'boy nuts about' is the wordplay.
'boy' becomes 'les' (short for Leslie).
'nuts' becomes 'mad' (I've seen this in other clues).
'about' shows that the letters should be reversed in order.
'les'+'mad'='lesmad'
'lesmad' back-to-front is 'DAMSEL'.
(Other definitions for damsel that I've seen before include "Young lady of old, perhaps in distress" , "Old-fashioned young woman" , "Maid" , "little fly" , "Someone in distress?" .)