Rough characters appear when Atletico and Arsenal meet (6)
I believe the answer is:
coarse
'rough' is the definition.
(associated in meaning)
I cannot understand how the rest of the clue works.
(Other definitions for coarse that I've seen before include "Boorish" , "Rough in texture or crude in manner" , "Rude, base" , "Rough, uncouth" , "needing refinement" .)