The setter and martial arts star brawl (5)
I believe the answer is:
melee
'brawl' is the definition.
(I've seen this before)
'the setter and martial arts star' is the wordplay.
'the setter' becomes 'me' (the person who set this crossword).
'and' says to put letters next to each other.
'martial arts star' becomes 'Lee' (Bruce Lee, 1940-1973).
'me'+'lee'='MELEE'
(Other definitions for melee that I've seen before include "Scrap" , "confused group" , "A confused fight or muddle" , "Confused fight or scuffle" , "Affray; muddled group" .)