Best mate knocked out by playwright (2,5,7)
I believe the answer is:
an ideal husband
'knocked out by playwright' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'best mate' is the wordplay.
I cannot really see how this works, but
'best' could be 'ideal' (similar in meaning) and 'ideal' is found in the answer.
'mate' could be 'husband' (husband is a kind of mate) and 'husband' is present in the answer.
The remaining letters 'an' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for an ideal husband that I've seen before include "Dramatic scenes involving perfect groom" , "Play by Oscar Wilde" , "comic drama" , "best man?" , "the perfect match?" .)