Terrible backlog, with backside of employee causing obstruction (8)
I believe the answer is:
blockage
'obstruction' is the definition.
(I know that blockage is a type of obstruction)
'terrible backlog with backside of employee' is the wordplay.
'terrible' indicates an anagram.
'with' means one lot of letters go next to another.
'backside of' indicates one should take the final letters.
The last letter of 'employee' is 'e'.
'backlog' is an anagram of 'blockag'.
'blockag'+'e'='BLOCKAGE'
'causing' acts as a link.
(Other definitions for blockage that I've seen before include "jam" , "Clot" , "Obstruction" .)