Drama training knight in enclosure (7)
I believe the answer is:
playpen
'enclosure' is the definition.
(playpen is a kind of enclosure)
'drama training knight' is the wordplay.
'drama' becomes 'play' ('play' can be a synonym of 'drama').
'training' becomes 'pe'.
'knight' becomes 'n' (chess).
'play'+'pe'+'n'='PLAYPEN'
'in' is the link.
(Other definitions for playpen that I've seen before include "Enclosure for kids" , "device to capture the young" , "juvenile restraint" , "Baby enclosure" , "Toddler's enclosure" .)