Useless writer's put up in it (5)
I believe the answer is:
inept
'useless' is the definition.
(thesaurus)
'writer's put up in it' is the wordplay.
'writer' becomes 'pen' (I've seen this before).
'put up' shows that the letters should be reversed in order.
'in' indicates putting letters inside.
'pen' backwards is 'nep'.
'nep' inserted within 'it' is 'INEPT'.
(Other definitions for inept that I've seen before include "Standard required in a piece of work (colloq.)" , "Clumsy - silly" , "Clumsy, out of place" , "lacks skill" , "Silly or senseless" .)