After brawl, dismiss one that may be on your back (8)
I believe the answer is:
rucksack
'one that may be on your back' is the definition.
'after brawl dismiss' is the wordplay.
'after' means one lot of letters go next to another.
'brawl' becomes 'ruck'.
'dismiss' becomes 'sack' ('sack' can be a synonym of 'dismiss').
'ruck' next to 'sack' is 'RUCKSACK'.
(Other definitions for rucksack that I've seen before include "Bergen?" , "Walker's pack" , "Trekker's baggage" , "Trekker's luggage" , "large bag" .)