Tackle criminal before con starts (4,1,2)

I believe the answer is:

have a go

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'tackle criminal' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for have a go that I've seen before include "Tackle criminal" , "Take a turn" , "Intervening to stop a criminal (colloq,)" , "Try (to help stop criminal?)" , "try to foil criminal" .)

I've seen this clue in The Independent.

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