Catching line, quickly thrown as safeguard (6)
I believe the answer is:
shield
'safeguard' is the definition.
(thesaurus)
'catching line quickly thrown' is the wordplay.
'catching' is an insertion indicator.
'line quickly' becomes 'l' (I am not sure about the 'quickly' bit.).
'thrown' becomes 'shied' (I've seen this before).
'l' inserted into 'shied' is 'SHIELD'.
'as' acts as a link.
Can you help me to learn more?
(Other definitions for shield that I've seen before include "where you may find your bearings" , "Protective cover" , "Protect or conceal" , "Protect, screen" , "Piece of armour carried on arm to protect body" .)