Crack habit fellow's lost (4)
I believe the answer is:
rock
'crack' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe there's a link between them I don't understand?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for rock that I've seen before include "Lull (baby); 50s pop" , "Perhaps Hudson" , "Large stone - type of music" , "Be unstable; lull (baby)" , "Sway - very big stone" .)