Game finally given outdoor enclosure (3)
I believe the answer is:
run
'outdoor enclosure' is the definition.
(area for animals to run around)
'game finally given' is the wordplay.
'game' becomes 'RU' (rugby union).
'finally' suggests the final letters.
The last letter of 'given' is 'n'.
'ru'+'n'='RUN'
(Other definitions for run that I've seen before include "Organize" , "goal for England player?" , "Path made by animals" , "Could be an extra" , "On the . . . - fleeing from pursuit" .)