Becomes awful when one takes aim (4,2,3)
I believe the answer is:
goes to pot
'awful when one takes aim' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'becomes' is the wordplay.
I cannot really understand how this works, but
'becomes' could be 'goes' ('go' can be a synonym of 'become') and 'goes' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for goes to pot that I've seen before include "Prepares to follow snooker player" , "Becomes bad" , "Become ruined" , "Approaches the snooker table" , "Deteriorates" .)