What Bristol supporter should do with great energy? (3,2,4)

I believe the answer is:

fit to bust

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'with great energy?' is the definition.
(fit to bust means with energy or enthusiasm)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for fit to bust that I've seen before include "What good bra should do" , "with extra energy" , "What correctly-selected bra will do" , "very excited?" .)

I've seen this clue in The Guardian.

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