Begins to make round enclosures (5)
I believe the answer is:
opens
'begins' is the definition.
(opening is a kind of begining)
'round enclosures' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'enclosures' becomes 'pens' (pen is a kind of enclosure).
'o'+'pens'='OPENS'
'to make' is the link.
(Other definitions for opens that I've seen before include "sports competitions" , "expands" , "Unfastens" , "Establishes" , "competitions welcoming all-comers" .)