Primarily, governance set in stone for sport (5)
I believe the answer is:
rugby
'for sport' is the definition.
(rugby is a kind of sport)
'primarily governance set in stone' is the wordplay.
'primarily' says to take the initial letters.
'set in' is an insertion indicator.
'stone' becomes 'ruby' (I've seen this before).
The first letter of 'governance' is 'g'.
'g' going inside 'ruby' is 'RUGBY'.
(Other definitions for rugby that I've seen before include "Tom Brown's school" , "Town in Warwickshire" , "The 13-a-side game" , "Team sport" , "English city; game" .)