Boy hugging the girl must be whipped (6)
I believe the answer is:
lashed
'whipped' is the definition.
('lash' can be a synonym of 'whip')
'boy hugging the girl' is the wordplay.
'boy' becomes 'lad' (lad is a kind of boy).
'hugging' indicates putting letters inside.
'the girl' becomes 'she' (**).
'lad' placed around 'she' is 'LASHED'.
'must be' acts as a link.
(Other definitions for lashed that I've seen before include "severely punished" , "Tied; whipped" , "Hit" , "Fastened securely" , "Verbally attacked" .)