Sideline, for example, filling report (8)
I believe the answer is:
relegate
'sideline' is the definition.
(I know that relegate is a is a more specific form of the action of sideline)
'example filling report' is the wordplay.
'example' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'filling' means one lot of letters goes inside another.
'report' becomes 'relate' (I've seen this before).
'eg' placed into 'relate' is 'RELEGATE'.
'for' is the link.
(Other definitions for relegate that I've seen before include "Transfer to a lower division" , "Move down to a lower grade" , "Move to a lower position" , "Assign to a lower position" , "Demote" .)