Not being upright, is giving a biased report (8)
I believe the answer is:
slanting
'biased report' is the definition.
'slanting' can be an answer for 'biased' (thesaurus). I am not sure about the 'report' bit.
'not being upright is giving a' is the wordplay.
I cannot really see how this works, but
'not' could be 'nt' (synonyms) and 'nt' is located in the answer.
'a' is within the answer.
The remaining letters 'sling' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for slanting that I've seen before include "Leaning, sloping" , "not on the level" , "Sloping, tilting" .)