Malformed sardines maybe, about a kilo netted (8)
I believe the answer is:
freakish
'malformed' is the definition.
(thesaurus)
'sardines maybe about a kilo netted' is the wordplay.
'sardines maybe' becomes 'fish' (sardine is a type of fish).
'about' becomes 'rea' (I've seen this in other clues).
'a kilo' becomes 'k' (phonetic alphabet: alpha, bravo, charlie etc.).
'netted' means one lot of letters goes inside another (inserted letters are caught or netted).
'rea'+'k'='reak'
'fish' enclosing 'reak' is 'FREAKISH'.
(Other definitions for freakish that I've seen before include "Extraordinarily unusual" , "Arbitrary" , "Very unexpected" , "Weird" .)