Rustle loose end (6)
I believe the answer is:
result
'end' is the definition.
(I've seen this in another clue)
'rustle loose' is the wordplay.
'loose' indicates an anagram (letters are loosened from their original positions).
'rustle' anagrammed gives 'RESULT'.
(Other definitions for result that I've seen before include "Rustle (anag.)" , "Verdict" , "Final score" , "Final outcome" , "Outcome of an undertaking" .)