Volunteers chess piece for capturing (6)
I believe the answer is:
taking
'for capturing' is the definition.
(I've seen this in another clue)
'volunteers chess piece' is the wordplay.
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'chess piece' becomes 'king' (king is a kind of chess piece).
'ta'+'king'='TAKING'
(Other definitions for taking that I've seen before include "Stealing; charming" , "Attractive" , "Harm, damage" , "Removal" , "Seizing, appropriating" .)