Shedding outside layer, initially making a defensive move (8)
I believe the answer is:
castling
'move' is the definition.
(castling is a kind of move)
'shedding outside layer' is the wordplay.
'shedding' becomes 'casting' ('cast' can be a synonym of 'shed').
'outside' is an insertion indicator (some letters go outside others).
'layer' becomes 'l' (this might be a standard abbreviation I've not previously seen).
'casting' going around 'l' is 'CASTLING'.
'initially making a defensive' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for castling that I've seen before include "Moving two men on board" , "chess move" , "defence of the board" .)