Not worth considering boxing fight shunned by beginner (3)
I believe the answer is:
out
'not worth considering' is the definition.
(I've seen this before)
'boxing fight shunned by beginner' is the wordplay.
'boxing fight' becomes 'bout'.
'shunned by beginner' means to remove the first letter.
'bout' with its initial letter removed is 'OUT'.
(Other definitions for out that I've seen before include "Published; unconscious" , "Dismissed, in cricket" , "Not allowed - on strike" , "Possibly caught" , "Heading back to the pavilion?" .)