Playwright Harold kennels old dog (7)
I believe the answer is:
pointer
'dog' is the definition.
(pointer is a kind of dog)
'playwright harold kennels old' is the wordplay.
I cannot really see how this works, but
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is found in the answer.
'playwright' could be 'pinter' (Harold Pinter) and 'pinter' is present in the remaining letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for pointer that I've seen before include "Arrow" , "Indicator" , "Smooth-haired game-dog" , "Hint (for a dog?)" , "helpful tip!" .)