Rough chisel possibly grabbed by broadcaster (7)
I believe the answer is:
sketchy
'rough' is the definition.
(both can mean vague)
'chisel possibly grabbed by broadcaster' is the wordplay.
'chisel possibly' becomes 'etch' (etch with a chisel).
'grabbed by' indicates putting letters inside (inserted letters are grabbed inside).
'broadcaster' becomes 'sky' (Sky is a broadcast TV channel).
'etch' placed within 'sky' is 'SKETCHY'.
(Other definitions for sketchy that I've seen before include "Vague" , "Not thorough or detailed" , "Barely outlined" , "first draft" , "Imprecise" .)