Support as friends come up to congratulate (8)

I believe the answer is:

backslap

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'congratulate' is the definition.
Although both the answer and definition are verbs in their base form, I don't understand how they can define each other.

'support as friends come up' is the wordplay.
'support as' becomes 'back' (synonyms. I am not sure about the 'as' bit.).
'friends' becomes 'pals' (pal is a kind of friend).
'come up' is a reversal indicator.
'pals' backwards is 'slap'.
'back'+'slap'='BACKSLAP'

'to' acts as a link.

Can you help me to learn more?

I've seen this clue in The Hindu.

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