Headed off mayhem with a gathering of fruit (7)
I believe the answer is:
avocado
'fruit' is the definition.
(I know that avocado is a type of edible fruit)
'headed off mayhem with a gathering' is the wordplay.
'headed off' means to remove the first letter.
'mayhem' becomes 'havoc' (synonyms).
'with' is a charade indicator (letters next to each other).
'gathering' becomes 'do' (party, social gathering of people).
'havoc' with its initial letter removed is 'avoc'.
'avoc'+'a'+'do'='AVOCADO'
'of' acts as a link.
(Other definitions for avocado that I've seen before include "Fruity colour" , "Tropical tree - edible green-skinned fruit" , "Are mostly outspoken party getting" , "Fruity type" , "may be stoned" .)