Writing groovy music for the film? (7)

I believe the answer is:

scoring

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'writing' is the definition.
(scoring is a kind of writing)

I can't explain the rest of the clue.

(Other definitions for scoring that I've seen before include "Gaining points" , "Arranging music" , "Writing music" , "Cutting - running" , "Winning points" .)

I've seen this clue in the Evening Standard.

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