This will break with martial artist coming round (4)
I believe the answer is:
dawn
'this will break' is the definition.
'dawn' can be an answer for 'break' (I have seen 'Break of day' mean 'dawn' so perhaps 'break' could also mean 'dawn'). I'm not sure about the 'this will' bit.
'with martial artist coming round' is the wordplay.
'with' becomes 'w' (abbreviation).
'martial artist' becomes 'dan' (I can't justify this - if you can you should believe this answer much more).
'coming round' means one lot of letters goes inside another.
'w' inserted into 'dan' is 'DAWN'.
Can you help me to learn more?
(Other definitions for dawn that I've seen before include "Daybreak" , "Break of day" , "Begin to appear" , "fresh start" , "Aurora was its goddess" .)