Good man holds one position (3)
I believe the answer is:
sit
'position' is the definition.
(I know that sit is a type of position)
'good man holds one' is the wordplay.
'good man' becomes 'st' (abbreviation for saint).
'holds' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'st' enclosing 'i' is 'SIT'.
(Other definitions for sit that I've seen before include "Take (an examination)" , "To take the test" , "Take a pew, an exam" , "Be sedentary" , "Rest on one's haunches" .)