One's posted eleven redrafts to capture action in theatre (8)
I believe the answer is:
envelope
'one's posted' is the definition.
(an envelope is put in the post)
'eleven redrafts to capture action in theatre' is the wordplay.
'redrafts' is an anagram indicator.
'to capture' indicates putting letters inside.
'action in theatre' becomes 'op' (operation - as in an operating theatre).
'eleven' is an anagram of 'envele'.
'envele' placed around 'op' is 'ENVELOPE'.
(Other definitions for envelope that I've seen before include "Outer covering" , "Even pole, strangely, can contain a letter" , "Item of mail" , "Coat" , "Wrapper for 31ac" .)