There's a snag with this type of song (5)

I believe the answer is:

catch

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'there's a snag' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for catch that I've seen before include "Disadvantage that's hidden" , "Fly in the ointment" , "Good match" , "potential partner?" , "Desirable partner" .)

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