Lets us organise fight (6)
I believe the answer is:
tussle
'fight' is the definition.
(I know that tussle is a kind of fight)
'lets us organise' is the wordplay.
'organise' is an anagram indicator (I've seen 'organised' mean this).
'lets'+'us'='letsus'
'letsus' with letters rearranged gives 'TUSSLE'.
(Other definitions for tussle that I've seen before include "Rough and tumble" , "Go at it" , "Lets us (anag) - fight" , "'Scuffle, rough-and-tumble (6)'" , "Sharp struggle" .)