Battle member, acting as witness (7)
I believe the answer is:
viewing
'acting as witness' is the definition.
I can't judge whether this defines the answer.
'battle member' is the wordplay.
'battle' becomes 'vie'.
'member' becomes 'wing' (wing is a kind of member).
'vie'+'wing'='VIEWING'
Can you help me to learn more?
(Other definitions for viewing that I've seen before include "What's done in front of the TV" , "Surveying" , "people in front of TV?" , "Opportunity to see" .)