Bridging loose to start with, cracked teeth wobble -- not fair! (5,3,4)

I believe the answer is:

below the belt

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'not fair' is the definition.
(I've seen this in another clue)

I cannot understand how the rest of the clue works.

(Other definitions for below the belt that I've seen before include "Foul landing place for blow" , "In an unfair manner" , "fly is here" , "dirty" , "Unsporting" .)

I've seen this clue in The Telegraph.

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