Clumsy error (7)
I believe the answer is:
blunder
'clumsy error' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for blunder that I've seen before include "Stupid mistake" , "A stupid 1 down" , "A clumsy mistake or movement" , "Careless mistake" , "Clumsy error" .)