Opposition recruit Napoli’s centre back (4)
I believe the answer is:
anti
'opposition' is the definition.
(I've seen this before)
'recruit napoli's centre back' is the wordplay.
'recruit napoli' becomes 'ant' (I can't justify this - if you can you should give a lot more credence to this answer).
'centre' says to take the centre.
'back' becomes 'spine' (synonyms).
The middle of 'spine' is 'i'.
'ant'+'i'='ANTI'
Can you help me to learn more?
(Other definitions for anti that I've seen before include "'No' voter" , "[NO MAN]" , "Opposition member" , "Policy's opponent" , "(Person who is) not in favour" .)