Be leaving rubble creating confused impression (4)
I believe the answer is:
blur
'confused impression' is the definition.
(I've seen this before)
'be leaving rubble creating' is the wordplay.
'leaving' suggests deleting specific letters.
'creating' indicates anagramming the letters.
'rubble' with 'be' removed is 'rubl'.
'rubl' is an anagram of 'BLUR'.
(Other definitions for blur that I've seen before include "Obfuscate" , "Obscure; smudge" , "Indistinct object - smudge" , "Out-of-focus image" , "Confused impression" .)