Silent left-hander's initial punches I sense, so brutal (9)
I believe the answer is:
noiseless
'silent' is the definition.
(I've seen this before)
'left-hander's initial punches i sense so brutal' is the wordplay.
I cannot really understand how this works, but
'left' could be 'l' (common abbreviation) and 'l' is found in the answer.
'i' is present in the answer.
'sense' could be 'nose' (nose is a kind of sense) and 'nose' is found within the remaining letters.
The remaining letters 'ess' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for noiseless that I've seen before include "unsound?" , "Lionesses (anag) - making no sound" , "Mum" , "Silent, quiet" , "with a silencer?" .)