Incompetent writer backs into it (5)
I believe the answer is:
inept
'incompetent' is the definition.
('inept' can be similar in meaning to 'incompetent')
'writer backs into it' is the wordplay.
'writer' becomes 'pen' (I've seen this before).
'backs' is a reversal indicator (I've seen 'back' mean this).
'into' indicates putting letters inside.
'pen' in reverse letter order is 'nep'.
'nep' going into 'it' is 'INEPT'.
(Other definitions for inept that I've seen before include "Incompetent or gauche" , "Unsuitable, clumsy" , "Standard required in a piece of work (colloq.)" , "Lacking skill" , "Absurd or unskilful" .)