Crab starter to spoil the family cat (8)
I believe the answer is:
sourpuss
'crab starter' is the definition.
'sourpuss' can be an answer for 'crab' (I've seen this before). I'm not sure about the 'starter' bit.
'spoil the family cat' is the wordplay.
'spoil the family' becomes 'sour' (I can't justify this - if you can you should give a lot more credence to this answer).
'cat' becomes 'puss' (puss is a kind of cat).
'sour'+'puss'='SOURPUSS'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for sourpuss that I've seen before include "Miserable so-and-so" , "Bad-tempered person" , "Miserable-looking person (or cat?)" , "Miserable, gloomy, type" , "Habitually sullen person" .)