Sort of thinking of belonging to the side (7)
I believe the answer is:
lateral
This clue is a double definition.
'sort of thinking' is the first definition.
(I've seen this before)
'belonging to the side' is the second definition.
(I've seen this before)
'of' is the link.
(Other definitions for lateral that I've seen before include "to one side" , "Relating to the side" , "Sort of thinking" , "One type of thinking" , "This kind of thinking is unconventional" .)