Foolishly lets us fight (6)
I believe the answer is:
tussle
'fight' is the definition.
(I know that tussle is a type of fight)
'foolishly lets us' is the wordplay.
'foolishly' indicates an anagram.
'lets'+'us'='letsus'
'letsus' is an anagram of 'TUSSLE'.
(Other definitions for tussle that I've seen before include "Struggle or wrestling match" , "'Scuffle, rough-and-tumble (6)'" , "Go at it" , "Skirmish" , "Lets us (anag) - fight" .)