Tool observed by poor writer (7)
I believe the answer is:
hacksaw
'tool' is the definition.
(hacksaw is a kind of tool)
'observed by poor writer' is the wordplay.
'observed' becomes 'saw' (seen).
'by' says to put letters next to each other.
'poor writer' becomes 'hack' (I've seen this in another clue).
'saw' after 'hack' is 'HACKSAW'.
(Other definitions for hacksaw that I've seen before include "metalworker may use?" , "something to cut copper?" , "One cuts" , "Metal-cutting tool" , "Blade in a frame under tension" .)