Party not settled? Seatbelt fastened incorrectly (9)
I believe the answer is:
beanfeast
'party' is the definition.
(beanfeast is a kind of party)
'not settled? seatbelt fastened incorrectly' is the wordplay.
'not' is a deletion indicator.
'incorrectly' indicates an anagram (I've seen this in other clues).
'seatbelt'+'fastened'='seatbeltfastened'
'seatbeltfastened' with 'settled' taken away is 'abfastene'.
'abfastene' is an anagram of 'BEANFEAST'.
(Other definitions for beanfeast that I've seen before include "Celebratory party" , "free meal" , "Party with lots of food and drink" .)