Crusading opponent with a career in tin-plating (7)
I believe the answer is:
saracen
'crusading opponent with a career in tin-plating' is the definition.
I can't judge whether this defines the answer.
'crusading opponent with a career in tin' is the wordplay.
'crusading opponent with' becomes 'a' (I can't justify this - if you can you should give a lot more credence to this answer).
'a career' becomes 'race' (career can mean to race around).
'in' indicates putting letters inside.
'tin' becomes 'Sn' (Sn is the chemical symbol for tin).
'a'+'race'='arace'
'arace' placed into 'sn' is 'SARACEN'.
Can you help me to learn more?
(Other definitions for saracen that I've seen before include "old Muslim back" , "Muslim defender in Crusades" , "Arab fighting the Crusades" , "Crusader's foe" , "Arab or Muslim at time of the Crusades" .)