A badly cracked container (4)
I believe the answer is:
safe
'container' is the definition.
(safe is a kind of container)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for safe that I've seen before include "Cash-box" , "Unharmed" , "Harmless" , "Out of harm's way" , "Secure cupboard" .)