Base of curling stone's round for game (5)
I believe the answer is:
rugby
'game' is the definition.
(rugby is a kind of game)
'base of curling stone's round' is the wordplay.
'base of' says to take the final letters.
'stone' becomes 'ruby' (I've seen this before**).
'round' means one lot of letters goes inside another.
The last letter of 'curling' is 'g'.
'g' placed inside 'ruby' is 'RUGBY'.
'for' acts as a link.
(Other definitions for rugby that I've seen before include "Famous public school" , "Game; town" , "Game named after school" , "Midlands town" , "Type of football; school" .)