Large birds surround king with boulders (5)
I believe the answer is:
rocks
'boulders' is the definition.
(I've seen this in another clue)
'large birds surround king' is the wordplay.
'large birds' becomes 'rocs' (I am not sure about this - if you are sure you should believe this answer much more).
'surround' indicates putting letters inside.
'king' becomes 'K' (abbreviation for king in chess).
'rocs' going around 'k' is 'ROCKS'.
'with' is the link.
Can you help me to learn more?
(Other definitions for rocks that I've seen before include "Lumps of hard mineral matter" , "Regular moves to get child off" , "Boulders" , "Causes shock to; diamonds" , "Crags; diamonds" .)