Try to hit the ball out of sight! (4)
I believe the answer is:
putt
'ball out of sight' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'try to hit the' is the wordplay.
'try to hit' becomes 'put' (I can't justify this - if you can you should believe this answer much more).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'put'+'t'='PUTT'
Can you help me to learn more?
(Other definitions for putt that I've seen before include "that's not needed if you chip in" , "Green stroke" , "Strike golf ball on green" , "Play ball on green" , "Golf stroke near hole" .)