Supporter in a cap (7)

I believe the answer is:

abetter

'supporter' is the definition.
(I've seen this before)

'a cap' is the wordplay.
'cap' becomes 'better' (I've seen this before).
'a'+'better'='ABETTER'

'in' acts as a link.

(Other definitions for abetter that I've seen before include "person giving encouragement" , "person to give encouragement?" , "One who encourages" , "Supporter" , "he helps you in trouble" .)

I've seen this clue in The Sunday Times and The Times.

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