Writer works hard knocking out one play (7)
I believe the answer is:
tolstoy
'writer' is the definition.
(I've seen this before)
'knocking out one play' is the wordplay.
'knocking' shows that the letters should be reversed in order.
'out one' becomes 'slot' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'play' becomes 'toy' (synonyms).
'slot' in reverse letter order is 'tols'.
'tols'+'toy'='TOLSTOY'
'works hard' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for tolstoy that I've seen before include "Author of Anna Karenina, d.1910" , "He wrote Anna Karenina" , "Count Leo . . . . . . . wrote 'War and Peace'" , "Lost toy belonging to Count Leo, writer" , "Russian novelist" .)