Saw guards beginning to like killing (7)
I believe the answer is:
slaying
'killing' is the definition.
(slaying is a kind of killing)
'saw guards beginning to' is the wordplay.
'saw' becomes 'saying' (a saw can mean a proverb or maxim).
'guards' is an insertion indicator (inserted letters are guarded).
'beginning to' becomes 'l' (I can't explain this - if you can you should give a lot more credence to this answer).
'saying' going around 'l' is 'SLAYING'.
'like' acts as a link.
Can you help me to learn more?
(Another definition for slaying that I've seen is " Killing".)