Crossword Genius

Muck in net turned over on Spanish beach (4,1,4)

Ross

I believe the answer is:

play a part

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

'net turned over on spanish beach' is the wordplay.
'net turned over' becomes 'part' (I can't justify this - if you can you should give a lot more credence to this answer).
'on' is a charade indicator (letters next to each other).
'spanish beach' becomes 'playa' (I've seen this before).
'part' after 'playa' is 'PLAY A PART'.

'in' acts as a link.

Can you help me to learn more?

(Other definitions for play a part that I've seen before include "Contribute" , "Be instrumental (in an activity)" .)

I've seen this clue in The Times.
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