Offence created by chap's giggles (12)
I believe the answer is:
manslaughter
'offence' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'by chap's giggles' is the wordplay.
'by' is a charade indicator (letters next to each other).
'chap's' becomes 'man's' (chap can mean a man).
'giggles' becomes 'laughter' (I can't explain this - if you can you should give a lot more credence to this answer).
'mans'+'laughter' is 'MANSLAUGHTER'.
'created' is the link.
Can you help me to learn more?
(Other definitions for manslaughter that I've seen before include "charge?" , "Killing without malice" , "Unlawful killing" , "slaying" , "Crime of unpremeditated killing" .)