Begin editing report, rubbing out rookie mistake (5)
I believe the answer is:
error
'mistake' is the definition.
(I know that mistake can be written as error)
'begin editing report rubbing out rookie' is the wordplay.
'begin' says to take the initial letters.
The first letters of 'editing report rubbing out rookie' is 'ERROR'.
(Other definitions for error that I've seen before include "Boob" , "Faulty judgment" , "Solecism" , "Mistake or fault" , "Slip, mistake" .)