Writer of The Third Man might be doing it in play (8)
I believe the answer is:
fielding
'writer' is the definition.
(I have seen 'British writer' mean 'fielding' so perhaps 'writer' could also mean 'fielding')
'the third man might be doing it in play' is the wordplay.
I cannot really see how this works, but
'man' could be 'field' and 'field' is found within the answer.
'in' is found in the answer.
A single letter 'g' remains which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for fielding that I've seen before include "What long leg is doing" , "slip?" , "Playing cricket; author" , "Perhaps trying to catch out" , "Dealing with" .)