To head off havoc, a party couple call for salad fruit (7,4)
I believe the answer is:
avocado pear
'salad fruit' is the definition.
'avocado pear' can be an answer for 'fruit' (avocado pear is a kind of fruit). I'm not sure about the 'salad' bit.
'to head off havoc a party couple call' is the wordplay.
'to head off' means to remove the first letter.
'party' becomes 'do' (do can informally mean a party).
'couple call' becomes 'pear' (I can't justify this - if you can you should give a lot more credence to this answer).
'havoc' with its first letter taken off is 'avoc'.
'avoc'+'a'+'do'+'pear'='AVOCADO PEAR'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for avocado pear that I've seen before include "Green-fleshed fruit" , "food item" , "Fruit with green-black skin and yellowish flesh" , "Fruit with green flesh" , "Basis of guacamole" .)