Crossword Genius

The catch that can mean trouble for the angler (4)

Ross

I believe the answer is:

snag

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

'the catch' is the definition.
(I've seen this in another clue)

'can mean trouble for the angler' is the wordplay.
I cannot really see how this works, but
'trouble' could be 'nag' (I've seen this in another clue) and 'nag' is found within the answer.
A single letter 's' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

'that' is the link.

Can you help me to learn more?

(Other definitions for snag that I've seen before include "Catch - disadvantage" , "Temporary hold-up" , "Stumbling block" , "Jagged projection" , "banger down under" .)

I've seen this clue in the Evening Standard.
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