The dog, Harold, is carrying a ball (7)
I believe the answer is:
pointer
'ball' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'the dog harold is carrying a' is the wordplay.
'the dog harold' becomes 'oint' (I am not sure about this - if you are sure you should believe this answer much more).
'is carrying' is an insertion indicator.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'oint' put into 'per' is 'POINTER'.
Can you help me to learn more?
(Other definitions for pointer that I've seen before include "Sign" , "Arrow" , "Smooth-haired game-dog" , "Game dog, used for its ability to scent" , "The dog provides an indication" .)