Crossword Genius

Plays a capricious part? (4,3,4)

Ross

I believe the answer is:

acts the goat

I'm a little stuck... Click here to teach me more about this clue!

'capricious part?' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'plays a' is the wordplay.
I cannot quite understand how this works, but
'plays' could be 'acts' ('act' can be a synonym of 'play') and 'acts' is found within the answer.
'a' is within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Irish Independent.
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