Part of the ground for the defender to keep an eye on (5,5)
I believe the answer is:
stand guard
'part of the ground' is the definition.
The answer and definition can be both to do with social activities as well as being verbs in their base form.
Perhaps there's an association between them I don't understand?
'the defender to keep an eye on' is the wordplay.
'the defender' becomes 'stand' (I can't justify this - if you can you should believe this answer much more).
'to keep an eye on' becomes 'guard' (guarding is a kind of keeping an eye on).
'stand'+'guard'='STAND GUARD'
'for' is the link.
Can you help me to learn more?
(Other definitions for stand guard that I've seen before include "Police" , "Act as sentry" , "Keep watch" .)