One highly apt to lead to a smash (3)
I believe the answer is:
lob
'a smash' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe you can see a link between them that I can't see?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for lob that I've seen before include "Fling" , "Throw ball in high arc" , "Toss" , "Chuck" , "Lofted ball" .)