A young woman has had bottom pinched, sadly (4)
I believe the answer is:
alas
'sadly' is the definition.
('alas' is used to express regret)
'a young woman has had bottom pinched' is the wordplay.
I cannot really see how this works, but
'a' is within the answer.
The remaining letters 'las' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for alas that I've seen before include "Archaic exclamation of sorrow or regret" , "-- and alack!" , "Cry of regret" , "Exclamation of misfortune" , "Antipodean island state" .)