Scribbler observed cutting tool (7)
I believe the answer is:
hacksaw
'cutting tool' is the definition.
(I've seen this before)
'scribbler observed' is the wordplay.
'scribbler' becomes 'hack' (I've seen this in another clue).
'observed' becomes 'saw' (seen).
'hack'+'saw'='HACKSAW'
(Other definitions for hacksaw that I've seen before include "Metal cutter" , "metalworker may use?" , "means of cutting lead article?" , "Blade in a frame under tension" , "Toothed tool for cutting metal" .)