A new shirt PC ordered — I’d retain his helmet? (9)
I believe the answer is:
chinstrap
'i'd retain his helmet?' is the definition.
I know that 'helmet' relates to this answer.
'a new shirt pc ordered' is the wordplay.
'new' becomes 'n'.
'ordered' indicates an anagram.
'a'+'n'+'shirt'+'pc'='anshirtpc'
'anshirtpc' with letters rearranged gives 'CHINSTRAP'.
(Other definitions for chinstrap that I've seen before include "Band" , "securing device" , "fastener" , "This secures cover for head" , "Bit of helmet" .)