Crossword Genius

Great activity produces maximum fluctuation (4,5)

Ross

I believe the answer is:

full swing

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

'great' is the definition.
Both the definition and answer are adjectives.
Maybe you can see a link between them that I don't see?

'activity produces maximum fluctuation' is the wordplay.
I cannot really understand how this works, but
'activity' could be 'swing' (swing is a kind of activity) and 'swing' is found in the answer.
The remaining letters 'full' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Globe and Mail.
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