Stressing, not getting enough goals, perhaps (12)

I believe the answer is:

underscoring

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'stressing' is the definition.
(underscoring is a kind of stressing)

'not getting enough goals perhaps' is the wordplay.
I cannot quite understand how this works, but
'not' could be 'un' (I've seen this in other clues) and 'un' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Telegraph.

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