Jack turned on one supporter at top of column (5)
I believe the answer is:
atlas
'column' is the definition.
(I know that atlas is a type of column)
'jack turned on one' is the wordplay.
'jack' becomes 'salt' (I can't justify this - if you can you should believe this answer much more).
'turned' says the letters should be written in reverse.
'on' means one lot of letters go next to another.
'one' becomes 'a' (a thing is one thing).
'salt' backwards is 'tlas'.
'tlas' after 'a' is 'ATLAS'.
'supporter at top of' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for atlas that I've seen before include "Holder of world" , "Asian satin" , "Map collection" , "God" , "Reference work" .)