Eccentric having dance with prison officer (9)
I believe the answer is:
screwball
'eccentric' is the definition.
(I know that screwball is a type of eccentric)
'dance with prison officer' is the wordplay.
'dance' becomes 'ball' (ball is a kind of dance).
'with' means one lot of letters go next to another.
'prison officer' becomes 'screw' (slang term).
'ball' put after 'screw' is 'SCREWBALL'.
'having' is the link.
(Other definitions for screwball that I've seen before include "touched person" , "Crazy (person)" , "odd fellow?" , "Card" , "Zany" .)