Rising head start for senior supporter (8)

I believe the answer is:

upholder

'supporter' is the definition.
(I know that upholder is a type of supporter)

'rising head start for senior' is the wordplay.
'rising' becomes 'up' (similar in meaning).
'start' suggests taking the first letters.
'for' says to put letters next to each other.
'senior' becomes 'older' (senior can mean the older of two people).
The initial letter of 'head' is 'h'.
'up'+'h'+'older'='UPHOLDER'

I've seen this clue in the Sydney Morning Herald.

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