Crusty end of a loaf (4)
I believe the answer is:
heel
'crusty end of a loaf' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for heel that I've seen before include "Call to dog" , "Untrustworthy person" , "Rogue" , "Rotten type" , "secure ball" .)