Bad average (4)
I believe the answer is:
mean
This clue is a double definition.
'bad' is the first definition.
(thesaurus)
'average' is the second definition.
(type of average)
(Other definitions for mean that I've seen before include "of little value" , "cause" , "Signify; miserly" , "Intend; stingy" , "Skilful" .)